imperfectly known, but appear to be related partly to Cuba, partly to
San Domingo, from each of which they are separated by a narrow channel
of very deep water. They are certainly not rich in the characteristic
groups of the Greater Antilles. The principal forms of _Helix_ are
_Plagioptycha_ (6 sp.), common with San Domingo, and _Hemitrochus_
(6 sp.), common with Cuba. _Strophia_ is exceedingly abundant, but
_Cylindrella_, _Macroceramus_, and _Glandina_ have but few species.
There are a few species of _Ctenopoma_, _Chondropoma_, and _Cistula_,
while a single _Schasicheila_ (absent from the rest of the sub-region)
forms a link with Mexico.
[Illustration: FIG. 229.--Characteristic Cuban Helices. =A=,
_Polydontes imperator_ Montf. =B=, _Caracolus rostrata_ Pfr. =C=,
_Polymita muscarum_ Lea.]
_Southern Florida_, with one or two species each of _Hemitrochus_,
_Cylindrella_, _Macroceramus_, _Strophia_, _Ctenopoma_, and
_Chondropoma_, belongs to this province.
(_b_) _Jamaica._--The land Mollusca of Jamaica are, in point of numbers
and variety, quite unequalled in the world. There are in all as many
as 56 genera and more than 440 species, the latter being nearly all
peculiar. The principal features are the Glandinae, the Helicidae,
and the land operculates. The Glandinae belong principally to the
sub-genera _Varicella_, _Melia_, and _Volutaxis_, _Streptostyla_ being
absent, although occurring in Cuba and San Domingo. There are 10 genera
of _Helix_, of which _Pleurodonta_ is quite peculiar, while _Sagda_
(13 sp.) is common only with S.W. San Domingo (2 sp.), and _Leptoloma_
(8 sp.) only with Cuba (1 sp.). The single _Strobila_ seems to be a
straggler from a N. American source. _Macroceramus_ has only 2 species
as against 34 in Cuba, and of _Cylindrella_, in which Cuba (130 sp.) is
so rich, only 36 species occur. The genus _Leia_, however (14 sp.), is
all but peculiar, occurring elsewhere only in the neighbouring angle
of San Domingo, which is so closely allied with Jamaica. The complete
absence of _Strophia_ is remarkable.
[Illustration: FIG. 230.--Characteristic Jamaican and Haitian
Mollusca: =A=, _Sagdae pistylium_ Müll., Jamaica; =B=,
_Chondropoma salleanum_ Pfr., San Domingo; =C=, _Eutrochatella
Tankervillei_ Gray, Jamaica; =D=, _Cylindrella agnesiana_ C. B.
Ad., Jamaica.]
The land operculates form the bulk of the land fauna, there being
actually 242 species, as against 221 of land Pulmonata, a proportion
never again approached in any part of the world. As many as 80 of
these belong to the curious little genus _Stoastoma_, which is all but
peculiar to the island, one species having been found in San Domingo,
and one in Porto Rico. _Geomelania_ and _Chittya_, two singular inland
forms akin to _Truncatella_, are quite peculiar. _Alcadia_ reaches
its maximum of 14 species, as against 4 species in San Domingo and 9
species in Cuba, and _Lucidella_ is common to San Domingo only; but, if
_Stoastoma_ be omitted, the Helicinidae generally are not represented
by so many or by so striking forms as in Cuba, which has 90 species, as
against Jamaica 44, and San Domingo 35.
(_c_) _San Domingo_, although not characterised by the extraordinary
richness of Cuba and Jamaica, possesses many specially remarkable forms
of land Mollusca, to which a thorough exploration, when circumstances
permit, will no doubt make important additions. From its geographical
position, impinging as it does on all the islands of the Greater
Antilles, it would be expected that the fauna of San Domingo would not
exhibit equal signs of isolation, but would appear to be influenced
by them severally. This is exactly what occurs, and San Domingo is
consequently, although very rich in peculiar species, not equally so in
peculiar genera. The south-west district shows distinct relations with
Jamaica, the Jamaican genera _Leia_, _Stoastoma_, _Lucidella_, and the
_Thaumasia_ section of _Cylindrella_ occurring here only. The north and
north-west districts are related to Cuba, while the central district,
consisting of the long band of mountainous country which traverses the
island, contains the more characteristic Haitian forms.
The Helicidae are the most noteworthy of the San Domingo land
Mollusca. The group _Eurycratera_, which contains some of the finest
existing land snails, is quite peculiar, while _Parthena_, _Cepolis_,
_Plagioptycha_, and _Caracolus_ here reach their maximum. The
Cylindrellidae are very abundant, but no section is peculiar. Land
operculates do not bear quite the same proportion to the Pulmonata
as in Cuba and Jamaica, but they are well represented (100 to 152);
_Rolleia_ is the only peculiar genus.
The relations of San Domingo to the neighbouring islands are
considerably obscured by the fact that they are well known, while San
Domingo is comparatively little explored. To this may perhaps be due
the curious fact that there are actually more species common to Cuba
and Porto Rico (26) than to Porto Rico and San Domingo. Cuba shares
with San Domingo its small-sized _Caracolus_ and also _Liguus_, but
the great _Eurycratera_, _Parthena_, and _Plagioptycha_ are wholly
wanting in Cuba. The land operculates are partly related to Cuba,
partly to Jamaica, thus _Choanopoma_, _Ctenopoma_, _Cistula_, _Tudora_,
and many others, are represented on all these islands, while the
Jamaican _Stoastoma_ occurs on San Domingo and Porto Rico, but not
on Cuba, and _Lucidella_ is common to San Domingo and Jamaica alone.
An especial link between Jamaica and San Domingo is the occurrence
in the south-west district of the latter island of _Sagda_ (2 sp.).
The relative numbers of the genera _Strophia_, _Macroceramus_, and
_Helicina_, as given below (p. 351), are of interest in this connexion.
_Porto Rico_, with Vièque, is practically a fragment of San Domingo.
The points of close relationship are the occurrence of _Caracolus_,
_Cepolis_, and _Parthena_ among the Helicidae, and of _Simpulopsis_,
_Pseudobalea_, and _Stoastoma_. _Cylindrella_ and _Macroceramus_
are but poorly represented, but _Strophia_ still occurs. The land
operculates (see the Table) show equal signs of removal from the
headquarters of development. _Megalomastoma_, however, has some
striking forms. The appearance of a single _Clausilia_, whose nearest
relations are in the northern Andes, is very remarkable. _Gaeotis_,
which is allied to _Peltella_ (Ecuador only), is peculiar.
[Illustration: FIG. 231.--Examples of West Indian Helices: =A=,
_Helix_ (_Parthena_) _angulata_ Fér., Porto Rico; =B=, _Helix_
(_Thelidomus_) _lima_ Fér., Vièque; =C=, _Helix_ (_Dentellaria_)
_nux denticulata_ Chem., Martinique.]
_Land Mollusca of the Greater Antilles_
Cuba. Jamaica. S. Domingo. Porto Rico.
Glandina 18 24 15 8
Streptostyla 4 ... 2 ...
Volutaxis ... 11 (?) 1 ...
Selenites 1 ... ... ...
Hyalinia 4 11 5 6
Patula 5 1 ... ...
Sagda ... 13 2 ...
Microphysa 7 18 8 3
Cysticopsis 9 6 ... ...
Hygromia (?) ... ... 3 ...
Leptaxis (?) ... ... 1 ...
Polygyra 2 ... ... ...
Jeanerettia 6 ... ... 1
Euclasta ... ... ... 4
Plagioptycha ... ... 14 2
Strobila ... 1 ... ...
Dialeuca ... 1 ... ...
Leptoloma 1 8 ... ...
Eurycampta 4 ... ... ...
Coryda 7 ... ... ...
Thelidomus 15 3 ... 3
Eurycratera ... ... 7 ...
Parthena ... ... 2 2
Cepolis ... ... 3 1
Caracolus 8 ... 6 2
Polydontes 3 ... ... 1
Hemitrochus 12 1 ... ...
Polymita 5 ... ... ...
Pleurodonta ... 34 ... ...
Inc. sed. 5 ... ... ...
Simpulopsis ... ... 1 1
Bulimulus 3 3 6 7
Orthalicus 1 1 ... ...
Liguus 3 ... 1 ...
Gaeotis ... ... ... 3
Pineria 2 ... ... 1
Macroceramus 34 2 14 3
Leia ... 14 2 ...
Cylindrella 130 36 35 3
Pseudobalea 2 ... 1 1
Stenogyra 6 7 (?) ...
Opeas 8 (?) 4 6
Subulima 6 14 2 2
Glandinella 1 ... ... ...
Spiraxis 2 (?) 2 1
Melaniella 7 ... ... ...
Geostilbia 1 ... 1 ...
Cionella 2 ... ... ...
Leptinaria ... 1 ... 3
Obeliscus ... ... 1 2
Pupa 2 7 3 2
Vertigo 4 ... ... ...
Strophia 19 ... 3 2
Clausilia ... ... ... 1
Succinea 11 2 5 3
Vaginula 2 2 2 1
Megalomastoma 13 ... 1 3
Neocyclotus 1 33(?) ... ...
Licina 1 ... 3 ...
Jamaicia ... 2 ... ...
Crocidopoma ... 1 3 ...
Rolleia ... ... 1 ...
Choanopoma 25 12 19 3
Ctenopoma 30 2 1 ...
Cistula 15 3 3 3
Chondropoma 57 (?) 19 4
Tudora 7 17 5 ...
Adamsiella 1 12 ... ...
Blaesospira 1 ... ... ...
Xenopoma 1 ... ... ...
Cistula 15 3 3 ...
Colobostylus 4 13 5 ...
Diplopoma 1 ... ... ...
Geomelania ... 21 ... ...
Chittya ... 1 ... ...
Blandiella ... ... 1 ...
Stoastoma ... 80 1 1
Eutrochatella 21 6 6 ...
Lucidella ... 4 1 ...
Alcadia 9 14 4 ...
Helicina 58 16 24 9
Proserpina 2 4 ... ...
The Virgin Is., with St. Croix, Anguilla, and the St. Bartholomew group
(all of which are non-volcanic islands), are related to Porto Rico,
while Guadeloupe and all the islands to the south, up to Grenada (all
of which are volcanic), show marked traces of S. American influence.
St. Kitt’s, Antigua, and Montserrat may be regarded as intermediate
between the two groups. St. Thomas, St. John, and Tortola have each
one _Plagioptycha_ and one _Thelidomus_, while St. Croix has two
sub-fossil _Caracolus_ which are now living in Porto Rico, together
with one _Plagioptycha_ and one _Thelidomus_ (sub-fossil). The gradual
disappearance of some of the characteristic greater Antillean forms,
and the appearance of S. American forms in the Lesser Antilles, is
shown by the following table:--
+-----------------------+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| | | | | | | | | | | | | | | S | | |
| | P | S | | | | | S | | G | | M | | | t | | |
| | o | t | | S | | | t | | u | | a | S | | . | | |
| | r | . | | t | | A | . | | a | D | r | t | B | | | T |
| | t | | S | . | T | n | | A | d | o | t | . | a | V | G | r |
| | o | T | t | | o | g | K | n | e | m | i | | r | i | r | i |
| | | h | . | C | r | u | i | t | l | i | n | L | b | n | e | n |
| | R | o | | r | t | i | t | i | o | n | i | u | a | c | n | i |
| | i | m | J | o | o | l | t | g | u | i | q | c | d | e | a | d |
| | c | a | a | i | l | l | ’ | u | p | c | u | i | o | n | d | a |
| | o | s | n | x | a | a | s | a | e | a | e | a | s | t | a | d |
| | . | . | . | . | . | . | . | . | . | . | . | . | . | . | . | . |
+-----------------------+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| Bulimulus | 7 | 4 | 2 | 4 | 1 | 2 | 2 | 3 | 8 | 9 | 5 | 3 | 3 | 6 | 2 | 4 |
| Cylindrella | 3 | 2 | 1 | 1 | 1 | . | . | . | 1 | . | 1 | 1 | 1 | . | . | 1 |
| Macroceramus | 3 | 1 | 1 | . | 2 | 1 | . | . | . | . | . | . | . | . | . | |
| Cyclostomatidae, etc. |23 | 4 | 1 | 5 | 1 | 1 | 1 | . | 4 | . | . | . | . | . | . | 1 |
| Dentellaria | . | . | . | . | . | . | 1 | 1 | 8 | 5 |11 | 2 | 2 | . | 1 | 1 |
| Cyclophorus | . | . | . | . | . | . | . | . | 1 | 2 | 2 | . | . | . | . | . |
| Amphibulimus | . | . | . | . | . | . | . | . | 2 | 3 | 1 | . | . | . | . | . |
| Homalonyx | . | . | . | . | . | . | . | . | 1 | 1 | . | . | . | . | . | . |
+---------------------------------------------------------------------------------------+
(_d_) In Guadeloupe we find _Cyclophorus_, _Amphibulimus_, _Homalonyx_,
and _Pellicula_, which are characteristic of S. America, and nearly
all recur in Dominica and Martinique. These islands are the metropolis
of _Dentellaria_, a group of _Helix_, evidently related to some of the
forms developed in the Greater Antilles. Stragglers occur as far north
as St. Kitt’s and Antigua, and there are several on the mainland as
far south as Cayenne. Traces of the great _Bulimus_, so characteristic
of South America, occur as far north as S. Lucia, where also is found
a _Parthena_ (San Domingo and Porto Rico). Trinidad is markedly S.
American; 55 species in all are known, of which 22 are peculiar, 28
are common to S. America (8 of these reach no farther north along the
islands), and only 5 are common to the Antilles, but not to S. America.
The occurrence of _Gundlachia_ in Trinidad has already been mentioned.
_The Bermudas_ show no very marked relationship either to the N.
American or to the West Indian fauna. In common with the former they
possess a _Polygyra_, with the latter (introduced species being
excluded) one species each of _Hyalosagda_, _Subulina_, _Vaginula_, and
_Helicina_, so that, on the whole, they may be called West Indian. The
only peculiar group is _Poecilozonites_, a rather large and depressed
shell of the _Hyalinia_ type.
(2) =The Central American Sub-region= may be regarded as extending
from the political boundary of Mexico in the north to the isthmus of
Panama in the south. It thus impinges on three important districts--the
N. American, West Indian, and S. American; and it appears, as we
should perhaps expect, that the two latter of these regions have
considerably more influence upon its fauna than the former. Of the
N. American Helicidae, _Polygyra_ is abundant in Mexico only, and
two species of _Strobila_ reach N. Guatemala, while the Californian
_Arionta_ occurs in Mexico. S. American Helicidae, in the sub-genera
_Solaropsis_ and _Labyrinthus_, occur no farther north than Costa Rica.
Not a single representative of any of the characteristic West Indian
Helicidae occurs. _Bulimulus_ and _Otostomus_, which form so large a
proportion of the Mollusca of Venezuela, Colombia, Ecuador, and Peru,
together with _Orthalicus_, are abundant all over the region. Again,
_Cylindrella_, _Macroceramus_, and some of the characteristic Antillean
operculates, are represented, their occurrence being in most cases
limited to the eastern coast-line and eastern slope of the central
range.
Besides these external elements, the region is rich in indigenous
genera. Central America is remarkable for an immense number of large
carnivorous Mollusca possessing shells. There are 49 species of
_Glandina_, the bulk of which occur in eastern and southern Mexico; 36
of _Streptostyla_ (S.E. Mexico and Guatemala, only 1 species reaching
Venezuela and another Peru); 5 of _Salasiella_, 2 of _Petenia_, and 1
of _Strebelia_; the last three genera being peculiar. _Streptaxis_,
fairly common in S. America, does not occur. _Velifera_ and
_Cryptostracon_, two remarkable slug-like forms, each with a single
species, are peculiar to Costa Rica. Among the especial peculiarities
of the region are the giant forms belonging to the Cylindrellidae,
which are known as _Holospira_, _Eucalodium_, and _Coelocentrum_ (Fig.
232). They are almost entirely peculiar to Mexico, only 7 out of a
total of 33 reaching south of that district, and only 1 not occurring
in it at all.
[Illustration: FIG. 232.--Examples of characteristic Mexican
Mollusca: =A=, _Coelocentrum turris_ Pfr.; =B=, _Streptostyla
Delattrei_ Pfr.]
The land operculates are but scanty. _Tomocyclus_ and _Amphicyclotus_
are peculiar, and _Schasicheila_, a form of _Helicina_, occurs
elsewhere only in the Bahamas. _Ceres_ (see Fig. 18, C, p. 21) and
_Proserpinella_, two remarkable forms of non-operculate Helicinidae
(compare the Chinese _Heudeia_), are quite peculiar. _Pachychilus_, one
of the characteristic fresh-water genera, belongs to the S. American
(Melaniidae) type, not to the N. American (Pleuroceridae). Among the
fresh-water Pulmonata, the _Aplecta_ are remarkable for their great
size and beauty. In the accompanying table “Mexico” is to be taken as
including the region from the United States border up to and including
the isthmus of Tehuantepec, and “Central America” as the whole region
south of that point.
_Land Mollusca of Central America_
Mexico only. Central Common to
America both.
only.
Strebelia 1 ... ...
Glandina 33 13 3
Salasiella 4 ... 1
Streptostyla 18 12 6
Petenia ... 1 1
Limax ... 1 ...
Velifera ... 1 ...
Omphalina 10 1 1
Hyalinia 2 5 3
Guppya ... 8 3
Pseudohyalina 2 ... 2
Tebennophorus 1 ... ...
Cryptostracon ... 1 ...
Xanthonyx 4 ... ...
Patula 3 ... 4
Acanthinula 1 2 2
Vallonia ... 1 ...
Trichodiscus 2 2 3
Praticolella 1 ... 1
Arionta 3 ... ...
Lysinoe 1 1 1
Oxychona 2 5 ...
Solaropsis ... 2 ...
Polygyra 14 1 2
Strobila 1 1 ...
Labyrinthus ... 5 ...
Otostomus 23 20 7
Bulimulus 6 5 2
Berendtia 1 ... ...
Orthalicus 6 3 3
Pupa 1 1 1
Vertigo 1 ... ...
Holospira 12 ... ...
Coelocentrum 6 1 1
Eucalodium 15 ... 5
Cylindrella 6 4 ...
Macroceramus 2 1 ...
Simpulopsis 2 1 ...
Caecilianella 1 ... ...
Opeas 1 2 3
Spiraxis 8 2 1
Leptinaria ... 2 ...
Subulina 2 3 4
Succinea 11 3 1
Vaginula 1 ... ...
Aperostoma ... 4 1
Amphicyclotus 2 1 2
Cystopoma 2 ... ...
Tomocyclus ... 1 2
Choanopoma 2 2 ...
Chondropoma 2 11 ...
Helicina 13 10 6
Schasicheila 2 ... 1
Ceres 2 ... ...
Proserpinella 1 ... ...
(3) =The Colombian Sub-region= includes Colombia, New Grenada,
Venezuela, Guiana, Ecuador, Peru, and Bolivia. It has been usual to
separate off the two latter countries as forming a distinct “Peruvian”
sub-region; but there is, as will be seen, absolutely no line to be
drawn between the Mollusca of Peru and those of Ecuador; nor would
one, on geographical considerations, expect to be able to draw such
a line. A better method of subdivision, so far as the species of the
whole eastern portion of the region are concerned, would be to group
the Mollusca according to the altitude at which they occur, were it not
that the evidence on this point is at present but fragmentary. We know,
however, that all along the line of the Andes certain species, more
particularly of _Bulimulus_, occupy their own zones of elevation, some
ascending as high as 10,000 feet above the sea, and never occurring on
the plains.
In the northern portions of this sub-region, Central American and West
Indian influence is felt to a certain extent. Thus there are eight
_Glandina_ and one _Streptostyla_ in Venezuela and Colombia together
with one or two species of _Cistula_, _Chondropoma_, _Proserpina_, and
_Cylindrella_, while a single _Strophia_ (decidedly a straggler) occurs
at Curaçao. In Demerara and Cayenne there are three or four species
of _Dentellaria_. In Ecuador, however, _Glandina_ diminishes to three
species, and in Peru disappears altogether, although one _Streptostyla_
occurs. Similarly the West Indian operculates are reduced to one
_Chondropoma_ (Ecuador) and disappear entirely in Peru.
[Illustration: FIG. 233.--=A=, _Orthalicus Deburghiae_ Reeve,
Ecuador; =B=, _Bulimus_ (_Pachyotus_) _egregius_ Jay, Brazil.]
The Helicidae are most abundant in the north and west, and are
represented by several very striking sub-genera, some of which possess
remarkably toothed apertures, and perhaps betray an ancestry common to
some of the West Indian genera. Of these, _Labyrinthus_ has 12 species
in Venezuela and Colombia, 5 in Ecuador, and 3 in Peru and Bolivia;
_Isomeria_ 12 in Venezuela and Colombia, 20 in Ecuador, and 2 in Peru
and Bolivia; _Salaropsis_ is represented in these countries by 6, 3,
and 7 species, and _Systrophia_ by 4, 5, and 8 species respectively.
_Clausilia_--in the group _Nenia_--appears in some numbers along the
Andes chain, the only other representative in the New World being the
solitary species occurring at Porto Rico. There have been described,
from Venezuela and Colombia 10 species, from Ecuador 5, and from Peru
and Bolivia 12.
Another marked feature of the region is the occurrence of the
Orthalicidae, in the two genera _Orthalicus_ and _Porphyrobaphe_.
The latter of these magnificent forms is peculiar, while the former
reaches Mexico, the West Indies, and Brazil. Ecuador, which contains 23
species, seems the metropolis of the group.
_Bulimus_ and _Bulimulus_, the former genus being peculiar to S.
America and the adjacent islands, are largely represented, the former
in the three groups _Borus_, _Dryptus_, and _Orphnus_. These attain
their maximum in Peru, with 25 species, but Venezuela and Colombia have
as many as 17. _Bulimulus_ has been subdivided into a number of groups,
_e.g._ _Drymaeus_, _Mesembrinus_, _Thaumastus_, _Mormus_, _Scutalus_,
with many others,--the exact scientific limits of which are not easily
discernible. It must suffice here to state that Peru seems to be the
headquarters of the group with about 190 species (which probably may
well be reduced), Ecuador having about 70, and Venezuela and Colombia
between 80 and 90.
[Illustration: FIG. 234.--_Rhodea gigantea_ Mouss., New Grenada.]
Two very remarkable forms belonging to the Pupidae, _Anostoma_ (Fig.
154, p. 248) and _Tomigerus_, occur in Venezuela, the metropolis.
_Rhodea_, another very peculiar shell (Fig. 234), whose exact family
position is uncertain, is peculiar to New Grenada. The land operculates
are few in number, and in Bolivia almost disappear. They belong
principally to _Neocyclotus_ (of which 11 species occur in Venezuela
and Colombia) and _Helicina_ (10 species in the same district),
besides the stragglers already mentioned from West Indian sources, and
a few _Cyclophorus_. _Bourcieria_ is a form of _Helicina_ peculiar
to Ecuador. _Ampullaria_, with _Ceratodes_, a peculiar planorbiform
sub-genus, and _Hemisinus_, form the bulk of the fresh-water
operculates.
_The Galapagos._--Thirty-four species of land Mollusca, all peculiar,
are known from these islands; 25 of these are forms of _Bulimulus_.
There are no Helicidae, one each of _Hyalinia_, _Leptinaria_, and
_Helicina_, and two _Pupa_. The _Bulimulus_ are mostly of the group
_Nesiotis_, and in their brown colour bear some outward resemblance to
the dark _Achatinella_ of the Sandwich Is., living as they do mostly
under scoriae on the ground, and not on trees. In type, however, they
appear to be derived from Chili and Peru, rather than from the parts
of S. America immediately contiguous. Another section (_Pleuropyrgus_
2 sp.) closely resembles a marine _Chemnitzia_. The islands are all
volcanic, and are probably not the result of subsidence; thus the
existing species are not to be regarded as the relics of a more
widespread fauna, but as a new set of inhabitants.
(4) =The Brazilian Sub-region.=--This immense district is very
little known, except in the south, and it is consequently impossible
to give any satisfactory account of its Mollusca. It is possible
that eventually it will be found that it falls into provinces
which correspond more or less to (_a_) the Amazon basin; (_b_) the
mountainous district in the east, drained by the Tocantins and the San
Francisco; (_c_) the Parana basin in the south central district; and
(_d_) the Argentine or Pampas district in the extreme south. But at
present the data are insufficient to establish any such subdivisions,
whose existence, if proved, would have an important bearing on the
problem of the coalescence of S. America into its present form.[379]
The Agnatha are represented by _Streptaxis_ alone (17 sp.). _Helix_ is
rare, but includes the peculiar _Polygyratia_ (Fig. 150 A, p. 246),
while _Labyrinthus_ (2 sp.), _Solaropsis_ (5 sp.), and _Systrophia_
are common with the Colombian Sub-region, and _Oxychona_ (4 sp.) with
the Central American. _Bulimus_ has in all 36 species, the sub-genera
_Pachyotus_ (Fig. 233) and _Strophochilus_ being peculiar. _Bulimulus_,
though not so abundant as in Peru and Ecuador, has about 60 species, of
which _Navicula_ (Fig. 235) is the most remarkable group. _Megaspira_
is peculiar. _Orthalicus_ has only 4 species, while _Tomigerus_ (4 sp.)
and _Anostoma_ (3 sp.) are common with Venezuela. Land operculates are
scarce, and appear to include only _Neocyclotus_, _Cyclophorus_, and
_Helicina_.
In Argentina, which may probably rank as a separate province, the
tropical forms greatly decrease, _Streptaxis_ being reduced to
2 species, and _Bulimus_ and _Bulimulus_ together to 40, while
_Orthalicus_, the great Helices, and the land operculates disappear
altogether. _Odontostomus_ (Fig. 236), a genus of the Pupidae, is
abundant in the northern part of the province. Two or three species of
_Chilina_ occur.
[Illustration: FIG. 235.--_Bulimulus_ (_Navicula_) _navicula_
Wagn., Brazil.]
[Illustration: FIG. 236.--_Odontostomus pantagruelinus_ Moric.,
S. Brazil. × ½.]
(5) =The Chilian Sub-region.=--The greater part of Chili, from its
arid and rainless climate, is unfavourable to the existence of land
Mollusca. _Bulimus_ (_Borus_) still has 3 or 4 species, and _Bulimulus_
(_Plectostylus_ 11, _Scutalus_ 9, _Peronaeus_ 7) is fairly abundant,
but the profusion of the tropics is wanting. There are no carnivorous
genera, and only two land operculates. A remarkable form of _Helix_
(_Macrocyclis_, Fig. 237) is quite peculiar, but the majority of
the species belong to two rather obscure groups, _Stepsanoda_ and
_Amphidoxa_. _Chilina_, a singularly solid form of _Limnaea_ (of which
8 sp., with a sub-genus _Pseudochilina_, occur in Chili), is peculiar
to Chili, S. Brazil, and Patagonia. From the two islands of _Juan
Fernandez_ and _Masafuera_, are known several _Helix_, of Chilian
affinity, several curious _Succinea_, a _Homalonyx_, _Leptinaria_,
and _Nothus_, and three species of _Tornatellina_, with the almost
universal _Limax gagates_.
The question of the existence at some remote period of a Neantarctic
continent, which formed a communication between the three great
southern peninsulas of the world, is one on which the Mollusca may
offer evidence. Von Ihering holds that an essential difference can be
observed between certain of the Unionidae which inhabit S. America,
Africa, and Australia with New Zealand, and those which inhabit
Europe, Asia, and N. America, but the point can hardly be regarded as
definitely established at present. Something perhaps may be made of
the distribution of _Bulimus_ and _Bulimulus_. It seems difficult to
explain the occurrence of sub-fossil _Bulimus_ on St. Helena except
on some such lines as have been recently adduced to account for the
presence of struthious birds in the Mascarenes, and possibly the
form _Livinhacea_ may be a trace of the same element in S. Africa.
Again, the _Liparus_ of S. and W. Australia, with the _Caryodes_ of
Tasmania, and the _Leucotaenia_ and _Clavator_ of Madagascar (which
all may be related to _Bulimus_), together with the _Placostylus_ of
New Caledonia and the adjacent islands, reaching even to New Zealand,
and perhaps even the _Amphidromus_ of Malaysia (which are more akin to
_Bulimulus_), may be thought to exhibit, in some remote degree, traces
of a common ancestry.
The land operculates give no help, and, of the carnivorous genera,
_Rhytida_ is a marked link between Africa and Australia, while
_Streptaxis_ is equally so between S. America and Africa. As regards
fresh-water Gasteropoda, _Ampullaria_ is common to S. America and
Africa, while _Isidora_ is common to Africa, Australia, and New
Zealand, but is altogether absent from S. America. _Gundlachia_ occurs
in Florida, Trinidad, and Tasmania, but has not been detected in
Africa. It must be concluded, therefore, that the present state of
the evidence which the Mollusca can afford, while exhibiting certain
curious points of relationship between the three regions in question,
is insufficient to warrant any decided conclusion.
[Illustration: FIG. 237.--_Macrocyclis laxata_ Fér., Chili.]
CHAPTER XII
DISTRIBUTION OF MARINE MOLLUSCA--DEEP-SEA MOLLUSCA
AND THEIR CHARACTERISTICS
Marine Mollusca may be divided roughly into Pelagic and non-Pelagic
genera. To the former division belong all Pteropoda and Heteropoda, and
a large number of Cephalopoda, together with a very few specialised
forms of Gasteropoda (_Ianthina_, _Litiopa_, _Phyllirrhoe_, etc.).
Pelagic Mollusca appear, as a rule, to live at varying depths below
the surface during the day, and to rise to the top only at night. The
majority inhabit warm or tropical seas, though some are exceedingly
abundant in the Arctic regions; _Clione_ and _Limacina_ have been
noticed as far north as 72°.[380]
The vertical range of Pelagic Mollusca has received attention from
Dr. Murray of the _Challenger_, Professor Agassiz of the _Blake_ and
_Albatross_, and others. Agassiz appears to have established the fact
that the surface fauna of the sea is limited to a comparatively narrow
belt of depth, and that there is no intermediate belt of animal life
between creatures which live on or near the bottom and the surface
fauna. Pelagic forms sink to avoid disturbances of various kinds,
to depths not much exceeding 150 to 200 fathoms, except in closed
seas like the Gulf of California and the Mediterranean, where the
bathymetrical range appears to be much greater.[381]
Non-Pelagic Mollusca are, from one point of view, conveniently
classified according to the different _zones of depth_ at which
they occur. Thus we are enabled to distinguish Mollusca of (_a_)
the _littoral_, (_b_) the _laminarian_, (_c_) the _nullipore_, or
_coralline_, and (_d_) the _abyssal_ zones. It must be borne in mind,
however, that these zones cannot be exactly defined, and that while the
littoral zone may be understood to imply the area between tide-marks,
and the abyssal zone a depth of 500 fathoms and upwards, the limits
between the laminarian and the coralline, and between the coralline and
abyssal zones can only be fixed approximately.
The difficulty of assigning special genera or species to special
‘zones of depth’ is increased by two important facts in the phenomena
of distribution. In the first place, it is found that species which
occur in shallow water in northern seas often extend to very deep
water in much lower latitudes. This interesting fact, which shows
the importance of temperature in determining distribution, was first
established by the dredgings of the _Lightning_ and _Porcupine_ off
the western coasts of Europe. In the second place, a certain number
of species seem equally at home in shallow and in abyssal waters, in
cases where a great difference of latitude does not occur to equalise
the temperature. Thus the _Challenger_ found _Venus mesodesma_ living
on the beach (New Zealand) and at 1000 fath. (Tristan da Cunha); _Lima
multicostata_ in ‘shallow water’ (Tonga and Port Jackson) and at 1075
fath. (Bermuda); _Scalaria acus_ from 49 to 1254 fath. (N. Atlantic);
and _S. hellenica_ from 40 to 1260 fath. (Canaries). The _Lightning_
and _Porcupine_ found, or record as found,[382] _Anomia ephippium_
at 0 to 1450 fath., _Pecten groenlandicus_ at 5 to 1785 fath., _Lima
subauriculata_ at 10 to 1785 fath., _Modiolaria discors_ at 0 to 1785
fath., _Crenella decussata_ at 0 to 1750 fath., _Dacrydium vitreum_
at 30 to 2750 fath., _Arca glacialis_ at 25 to 1620 fath., _Astarte
compressa_ at 3 to 2000 fath., and _Scrobicularia longicallus_ at 20 to
2435 fath. _Puncturella noachina_ has been found at 20 to 1095 fath.,
_Natica groenlandica_ at 2 to 1290 fath., _Rissoa tenuisculpta_ at 25
to 1095 fath. In many of these cases we are assured that no appreciable
difference can be detected between specimens from the two extremes of
depth.
In spite, however, of these remarkable vagaries on the part of certain
species, we are enabled roughly to distinguish a large number of
genera as ‘shallow-water’ and ‘deep-water’ respectively, while a still
larger number occupy an intermediate position. Among shallow-water
genera may be named _Patella_, _Littorina_, _Nassa_, _Purpura_,
_Strombus_, _Haliotis_, _Mytilus_, _Cardium_, _Solen_; while among
deep-water genera are _Pleurotoma_, _Scissurella_, _Seguenzia_,
_Dentalium_, _Cadulus_, _Limopsis_, _Nucula_, _Leda_, _Lima_, and
_Axinus_.
Theories on the geographical distribution of marine Mollusca have been
revolutionised by the discoveries of recent exploring expeditions.
The principal have been those of Torell (Swedish) (1859–61) on the
coasts of Greenland and Spitzbergen; of the _Lightning_ and _Porcupine_
(British) in 1868–70, in the N.E. Atlantic, off the Scotch, Irish,
French, and Portuguese coasts, and in the Mediterranean; of the
_Challenger_ (British), under Sir C. Wyville Thomson, in 1873–76,
in which all the great ocean basins were dredged or sounded; of the
_Blake_ (American), under Alexander Agassiz, in 1877–80, in the West
Atlantic, Gulf of Mexico, and Caribbean Seas; of the _Travailleur_
(French) in 1880–83, off the west coasts of France, Portugal, and
Morocco, Madeira, the Canaries, and the Golfe du Lion; of the
_Talisman_ (French) in 1882, off the west coast of Africa from Tangier
to Senegal, the Atlantic Islands, and the Sargasso Sea; of the
_Albatross_ (American) in 1891, off the west coast of tropical America;
of several other vessels belonging to the U.S. Fish Commission and
Coast Survey, off east American shores; and of the Prince of Monaco in
the _Hirondelle_ and _Princesse Alice_ at the present time, in the N.
Atlantic and Mediterranean.
The general result of these explorations has been to show that the
marine fauna of very deep water is much the same all the world
over, and that identical species occur at points as far removed as
possible from one another. The ocean floor, in fact, with its uniform
similarity of temperature, food, station, and general conditions of
life, contains no effectual barrier to the almost indefinite spread
of species.[383] To give a few instances. The _Challenger_ dredged
_Silenia Sarsii_ in 1950 fath., 1100 miles south-west of Australia,
and also in 2650 fath. off the mouth of the Rio de la Plata; _Semele
profundorum_ in 1125 fath. near the Canaries, and in 2900 fath. mid
N. Pacific; _Verticordia deshayesiana_ in 155 fath. near Cape York,
and in 350 fath. off Pernambuco; _Arca pteroessa_ in 2050 fath. mid N.
Pacific, in 1000–1675 fath. west of the Azores, and in 390 fath. off
the West Indies; _Arca corpulenta_ in 1400 fath. off N.E. Australia, in
2425 fath. mid-Pacific, and in 1375 fath. near Juan Fernandez; _Lima
goliath_ in 775 fath. off S. Japan, and in 245 fath. off S. Patagonia;
_Pleurotoma engonia_ in 700 fath. north-east of New Zealand, and in
345 fath. off Inoshima. A surprising range was occasionally found even
in shallow-water species; thus _Petricola lapicida_ was discovered
by the same expedition in the West Indies and N. Australia, _Cardita
calyculata_ off Teneriffe and in Bass Strait, _Arca imbricata_ off Cape
York and in the West Indies, _Modiolaria cuneata_ at Port Jackson and
Cape of Good Hope, _Lima squamosa_ at Teneriffe and the Philippines. In
these latter cases it is not improbable that the species lives in deep
water as well, from which it has not yet been dredged.
It follows from these considerations that any attempt to classify
marine Mollusca under Regions and Provinces can only apply to Mollusca
which occur at moderate depths. The most important factor in the
environment, as determining distribution, is the _temperature of the
water_, which is probably to be regarded as affecting not so much the
adult Mollusca as their ova; for the adult might possibly support
life under conditions in which the ova would perish. It appears that
a sudden change of temperature is the most effective barrier to
distribution,[384] and may bring the range of a species to an almost
instantaneous stop, while a very gradual change will allow it to extend
its range very widely.
It has been usual to classify marine Mollusca from moderate depths
under the following regions and sub-regions:--
Regions Sub-regions
{1. Arctic.
{2. Boreal.
=A.= =Atlantic= and {3. Celtic.
=Circumpolar= {4. Lusitanian.
{5. West African.
{6. South African.
=B.= =Indo-Pacific= {1. Indo-Pacific.
{2. Japanese.
=C.= =Australian= {1. Australian.
{2. Neozealanian.
{1. Aleutian.
{2. Californian.
{3. Panamic.
=D.= =American= {4. Peruvian.
{5. Magellanic.
{6. Argentinian.
{7. Caribbean.
{8. Transatlantic.
=A. The Atlantic Region=
includes the whole to the eastern shores of the Atlantic, from the
extreme north of the Cape of Good Hope, together with the circumpolar
seas, which may be regarded as roughly bounded by the Aleutian Islands
and the coast of Newfoundland.
(1) _The Arctic Sub-region_ includes the circumpolar seas, and is
bounded in the N. Pacific by a line drawn between Cape Avinoff in
Alaska, and Cape Lopatka in Kamchatka, so as to exclude the Aleutian
Islands. On the western shores of the Atlantic the cold Labrador
current brings it as far south as the coast of Newfoundland, but on
the eastern shores the influence of the Gulf Stream has the contrary
effect, so that the North Cape may be taken as its southern limit.
The principal genera (many species of which are common to the whole
sub-region) are _Volutomitra_, _Buccinum_, _Buccinopsis_, _Neptunea_,
_Trophon_, _Bela_, _Admete_, _Velutina_, _Trichotropis_, _Lacuna_,
_Margarita_, _Philine_, _Pecten_, _Leda_, _Yoldia_, _Astarte_, and
_Mya_. The shells are generally unicoloured, and of a dead white or
rather sombre tint.
(2) _The Boreal Sub-region_ may be subdivided into two provinces, the
European and the American. The former includes the entire coast-line
of Norway, the Färoe Islands, and Iceland (except perhaps the northern
coast), and possibly the Shetland Islands; the latter the American
coasts from the Gulf of St. Lawrence to Cape Cod (lat. 42°). Thus the
Boreal American province does not extend nearly so far south as the
Boreal European, the reason being that on the American coasts the
cold Labrador current, which hugs the land, bars back the advance of
southern genera, but allows Boreal genera to spread southwards, while
on the European side the warmer conditions produced by the Gulf Stream
keep the Boreal species back, and allow more southern forms to spread
northwards.
Many of the Boreal species occur on both sides of the Atlantic, and
thus support the theory of a more continuous fringe of continental land
once existing along the north of the Atlantic. Among the prominent
genera, besides several of those mentioned under the Arctic Sub-region,
are _Purpura_, _Chenopus_, _Littorina_, _Gibbula_, _Natica_, _Patella_,
_Tectura_, _Chiton_, _Doris_, _Aeolis_, _Tellina_, _Thracia_.
(3) _The Celtic Sub-region_ includes the British Islands (excepting
perhaps the Shetland Islands), the coasts of the North Sea and the
Baltic, with N. France to Cape Ushant. The absence of any cold or
warm current exerting direct influence upon the coast-line of this
sub-region causes a very gradual change in the conditions of life
as we move either southward or northward. The fauna of the British
seas contains a decided mixture of northern and southern forms. The
following are among the common Boreal species which attain their
southward range on our coasts: _Tectura testudinalis_ Müll. (to Dublin
Bay and Scarborough), _Trichotropis borealis_ Brod. (to the Dogger
Bank), _Margarita helicina_ Fabr. (to Yorkshire and Dublin Bay), _M.
groenlandica_ Chem. (western Scotland), _Natica montacuti_ Forb. (to
Cornwall), _Trophon truncatus_ Str. (to Tenby), _Chiton marmoreus_
Fabr. (to Dublin Bay and Scarborough). _Buccinum undatum_ and
_Littorina littorea_ become very scarce on our extreme south-western
coasts. Among Lusitanian species which reach our coasts are _Gibbula
magus_ L. (to Orkney and Shetland Islands), _Phasianella pullus_ L.
(to Caithness), _Galerus chinensis_ L. (to Milford Haven), _Galeomma
Turtoni_ Turt. (to Weymouth), _Cardium aculeatum_ L. (to Isle of Man),
_Solen vagina_ L. (to north Ireland).
It appears from the Mollusca of our Crag formations that at the
time of their deposition the temperature of our seas must have been
considerably warmer than it is now. Thus in the Crag we find many
species and even genera (_e.g._ _Mitra_, _Fossarus_, _Triton_,
_Vermetus_, _Ringicula_, _Chama_) which now occur no farther north
than the southern coasts of the Channel, the west of France, and the
Mediterranean.
The Baltic, a sea specially liable to violent changes of temperature,
with a large admixture of fresh water at its eastern end, appears to
possess only about 65 species in all. More than 50 genera occurring on
the western coasts of Denmark do not enter the Sound. In the eastern
portion of the Baltic marine and fresh-water species live together (p.
12).
(4) _The Lusitanian Sub-region_ extends from Cape Ushant in the north
to Cape Juby (lat. 28°) in the south, and includes the whole of the
Mediterranean, as well as the Azores, Canaries, and Madeira groups.
The English Channel acts as an effectual barrier to the northward
extension of many species; as many as 81 species which occur in
western France do not reach British coasts (P. Fischer). At the same
time, the western coasts of France are rather intermediate between
the two sub-regions than distinctly Lusitanian, for between 50 and 60
Mediterranean genera do not occur on those coasts.
The Mediterranean itself is exceedingly rich in species, about 1200
in all (including deep-water species) being known. A certain number
of these belong to tropical genera which here find their northern
limit, _e.g._ _Fasciolaria_, _Cancellaria_, _Sigaretus_, _Siliquaria_,
_Chama_, _Spondylus_. Here too occur _Carinaria_, _Lobiger_, _Oxynoe_,
_Pedicularia_, _Cypraea_, _Marginella_, _Mitra_, _Dolium_, _Cassis_,
_Cassidaria_, _Pisania_, _Euthria_, _Vermetus_, _Argonauta_, and many
others. A few Celtic and even Boreal species, which occur on the
western coasts of Morocco, do not enter the Mediterranean. Among these
are _Purpura lapillus_, _Helcion pellucidum_, and _Tellina balthica_.
_Halia_, a rare West African genus akin to _Pleurotoma_, is found in
Cadiz Bay, and the West African _Cymbium_ occurs on the Spanish coasts
as far as Malaga.
The Black Sea, whose northern and western coasts are exceedingly
cold, is comparatively poor in species. The Sea of Azof is chiefly
characterised by forms of _Cardium_.
(5) _The West African Sub-region_ extends from Cape Juby to a point
probably not very far south of lat. 30° S., the cold current which
sweeps up from the Pole probably limiting the southward extension of
tropical species on this side of Africa, while the warm Mozambique
current on the eastern side permits the spread of many Indo-Pacific
species almost as far south as the Cape. Owing to its extreme
unhealthiness, and the absence of harbours, the sub-region is very
little known.
The principal genera are _Cymbium_, _Pleurotoma_, _Marginella_,
_Terebra_, _Mitra_, _Agaronia_, _Murex_, _Cancellaria_, _Purpura_,
_Pseudoliva_, _Natica_, _Tellina_, _Lucina_, _Tugonia_, _Schizodesma_,
and _Arca_. Studer has enumerated as many as 55 species common to West
Africa and the opposite American shores. The north and south equatorial
currents, which circulate in this part of the Atlantic, probably
transport the larvae from one coast to the other. _Purpura coronata_
Lam., a characteristic West African species, is represented by a
well-marked variety in Demerara.
The Mollusca of St. Helena (178 known species) most resemble those of
the West Indies, 50 per cent being common, while 30 per cent are common
to the Mediterranean. From Ascension Island only 33 species are known,
which in their general relations resemble those of St. Helena.[385]
(6) _The South African Sub-region_ extends along the coast from about
lat. 30° on the west, to about East London on the east. Mr. G. B.
Sowerby enumerates 740 species from ‘South Africa,’ but includes in
this list Natal species, which more properly belong to the Indo-Pacific
fauna. Of these 740, 323 are peculiar, while 67 also occur in European
seas, some being familiar on our own shores. It is remarkable to
find in a sub-region separated from ourselves by the whole width
of the tropics, such well-known forms as _Mangilia costata_ Don.,
_M. septangularis_ Mont., _Cylichna cylindracea_ Penn., _Pholas
dactylus_ L., _Solen marginatus_ Pult., _Cultellus pellucidus_ Penn.,
_Ceratisolen legumen_ L., _Lutraria oblonga_ Chem., _Tellina fabula_
Gmel., _T. tenuis_ Da C., _Modiolaria discors_ L., and many others.
The leading genera are _Euthria_, _Triton_, _Cominella_, _Bullia_,
_Nassa_, _Cypraeovula_, _Oxystele_, _Fissurella_, _Fissurellidaea_,
_Patella_, and _Chiton_.
The Mollusca of Kerguelen Island and the Marion and Crozets groups
show relationship partly with South America, partly with the Cape, and
partly with South Australia and New Zealand, thus showing some trace
of a circumpolar antarctic fauna corresponding to, but not nearly so
well marked as that of the circumpolar arctic sub-region. Among the
remarkable forms discovered off Kerguelen are _Neobuccinum_ and a
sub-genus of _Struthiolaria_ (_Perissodonta_).
=B. The Indo-Pacific Region=
includes the whole of the coast-line of the Indian and western Pacific
oceans, from about East London in South Africa to the north of Niphon
(lat. 42°) in Japan, with the Red Sea and Persian Gulf, the whole of
the Indo-Malay Archipelago, Polynesia to the Sandwich Islands in the
north-east, and Easter Island in the south-east, and Australia to Swan
River in the west, and to Sandy Cape and Lord Howe’s Island in the
east. It is especially the region of coral reefs, which furnish so
favourite a home of the Mollusca, and which are entirely absent from
the Atlantic Region.
(1) _The Indo-Pacific Sub-region proper_ (which includes the whole of
this region except that part defined below as the Japanese Sub-region)
is by far the richest in the world. The marine Mollusca of the
Philippines alone (in some respects the nucleus of the whole region)
have been estimated at between 5000 and 6000 species, and Jousseaume
estimates Red Sea species at about 1000. Some prominent genera are
very rich in species. Garrett enumerates from Polynesia 81 species of
_Conus_, 60 of which occur on the Viti Is., 21 on the Sandwich Is.,
and only 14 on the Marquesas, where coral reefs are almost absent; 82
species of _Cypraea_, Viti Is. 44, Sandwich Is. 31, Marquesas only 13;
167 species of _Mitra_ (besides 29 recorded by others), Viti Is. 120,
Sandwich Is. 36, Marquesas 7. Of 50 existing species of _Strombus_, 39
occur in this region, and 10 out of 11 _Eburna_.
The following important genera are quite peculiar to the region:
_Nautilus_, several forms of Purpuridae, _e.g._ _Rapana_, _Magilus_,
_Rapa_, _Melapium_, and _Ricinula_; _Tudicla_, several forms of
Strombidae, _e.g._ _Rostellaria_, _Terebellum_, _Pteroceras_, and
_Rimella_; _Cithara_, _Melo_, _Neritopsis_, _Stomatia_, _Malleus_,
_Vulsella_, _Cucullaea_, _Tridacna_, _Hippopus_, _Libitina_,
_Glaucomya_, _Anatina_, _Aspergillum_, and many others.
The number of species common to the Red Sea and Mediterranean is
exceedingly small, some authorities even denying the existence of a
single common species. The present author, from an examination of the
shells dredged by MacAndrew at Suez, regarded 17 species as common, and
Mr. E. A. Smith has confirmed this view with regard to 8 of the species
in question.[386] The Mollusca occurring in Post-pliocene beds at Suez
show that Mediterranean species lived there in comparatively recent
geological times.
The opening of the Suez Canal appears to have already induced several
species to start on their travels from the Mediterranean to the Red Sea
and _vice versâ_. Two Red Sea species (_Mactra olorina_ Phil., _Mytilus
variabilis_ Kr.) had in 1882 established themselves at Port Said, while
two Mediterranean species (_Pholas dactylus_ L., _Solen vagina_ L.) had
reached Ismailia.[387]
(2) _The Japanese Sub-region_ consists of the Japanese Islands to
Niphon, together with Corea and a stretch of adjacent mainland coast of
unknown extent. The warm Kuro Siwo current, sweeping up between Luzon
and Formosa, permits tropical species to extend much farther north than
on the opposite shores of America, where a cold polar current keeps
them back. A certain number of species, however, are common to the
two shores of the Pacific, and a few circumpolar species occurring on
our own coasts reach Japan, _e.g.__Trophon clathratus_, _Puncturella
noachina_, _Mya arenaria_, _Modiola modiolus_, _Lasaea rubra_, and
_Nucula tenuis_.
Among the characteristic genera are _Fusus_, _Siphonalia_,
_Columbarium_, _Hemifusus_, _Rapana_, _Chlorostoma_, _Pleurotomaria_,
_Haliotis_, and _Cyclina_.
=C. The Australian Region=
includes the Australian coast-line from about Swan R.[388] (lat.
32° S.) to Sandy Cape (lat. 25° S.), Tasmania, New Zealand, and the
adjacent islands (except Lord Howe’s I.).
(1) _The Australian Sub-region proper_ (which consists of the whole
of the region excepting New Zealand and the adjacent islands) is
determined by the influence of the Antarctic Drift, which washes the
whole of the southern coasts of Australia, and runs strongly northward
between Australia and New Zealand. The E. Australian warm current from
the north is checked at Sandy Cape by this cold current, and flows off
to New Zealand, the western shores of which island are consequently
much warmer than the eastern. On the western coast of Australia the
Antarctic Drift has less force, and tropical genera accordingly range
some 7 degrees farther south on the western than on the eastern coasts.
The characteristic genera are _Voluta_ (of which half the known
species occur on Australian coasts[389]), _Cominella_, _Siphonalia_,
_Struthiolaria_, _Risella_, _Phasianella_, a number of genera belonging
to the Trochidae, _e.g._ _Liotia_, _Clanculus_, _Euchelus_, _Thalotia_,
_Elenchus_, _Trochocochlea_, _Zizyphinus_, _Bankivia_, _Trigonia_,
_Myodora_, _Myochama_, _Solenomya_, _Ephippodonta_, _Anapa_, _Mylitta_,
_Mesodesma_, and _Chamostrea_. _Trigonia_, originally discovered as
a recent form in Sydney Harbour (p. 65), is not peculiar to that
locality, occurring also off Cape York, West Australia, and Tasmania.
(2) _The Neozealanian Sub-region_ includes New Zealand, with the
outlying islands (Chatham, Auckland, and Campbell Is.).
As many as 455 species (Cephalopoda, 8; Gasteropoda, 311; Scaphopoda,
2; Pelecypoda, 134) have been enumerated by Professor F. W. Hutton as
occurring within the sub-region, of which only 64 are found elsewhere,
the proportion of peculiar species being thus nearly 86 per cent. New
Zealand therefore is, in its marine, no less than its land Mollusca,
greatly isolated.
The characteristic genera are _Anthora_, _Cryptoconchus_, and
_Vanganella_, which appear to be quite peculiar, _Trophon_,
_Cominella_, _Euthria_, most of the Trochidae also characteristic of
S. Australia, _Haliotis_, _Patella_, _Taria_, _Mesodesma_, _Mylitta_,
_Zenatia_, _Standella_, and _Myodora_.
=D. The American Region=
includes the entire coasts of North and South America with the adjacent
islands, south of Cape Avinoff on the western, and south of Cape Cod
on the eastern coast, the portions north of these points belonging to
the Arctic Sub-region.
(1) _The Aleutian Sub-region_ consists of the islands of Yesso and
Saghalien, with the adjacent shores of the Sea of Okhotsk to Cape
Lopatka, the Aleutian Is., and the west American coast from about Cape
Avinoff (lat. 60° N.) to St. Jean de Fuca Straits.
A certain number of species, probably of arctic origin, are common
with British and also with East American shores, the former being the
more numerous. Species as familiar to us as _Lacuna divaricata_ Fabr.,
_Trichotropis borealis_ Brod., _Pholas crispata_ L., _Mya truncata_ L.,
_M. arenaria_ L., _Mytilus edulis_ L., and _Modiolaria nigra_ Gray,
occur. The more characteristic genera are _Chrysodomus_, _Volutharpa_,
_Buccinum_, _Tectura_, _Scurria_, _Chiton_, _Cryptochiton_ (_Cr.
Stelleri_ Midd. is by far the largest known of the Chitonidae, 6 inches
long), _Tellina_ and _Pecten_.
(2) _The Californian Sub-region_ extends from St. Jean de Fuca Straits
(lat. 48° N.) to Cape St. Lucas, the Gulf of California belonging to
the Panamic sub-region. The northern polar current, which washes the
shores of this sub-region throughout their whole extent, prolongs the
southward range of the more northern genera, and keeps back those more
markedly tropical, the latter, however, creeping northward in the
warmer waters of the Gulf of California. Some authorities subdivide
this immense stretch of coast-line, as characterised by sub-temperate,
temperate, and sub-tropical genera, into the Oregonian, Californian,
and Lower Californian provinces.
The characteristic genera are--in the north, _Argobuccinum_,
_Zizyphinus_, _Chlorostoma_, _Tectura_, _Scurria_, _Chiton_
(_Katharina_, _Mopalia_, _Tonicia_), _Cryptochiton_, _Placunanomia_,
and _Mytilimeria_; in the centre, _Purpura_, _Monoceros_, _Amphissa_,
_Norrisia_, _Platyodon_, _Tapes_, and _Macoma_; and, towards the south,
_Olivella_, _Chorus_, _Macron_, _Pseudoliva_, _Trivia_, and _Haliotis_.
(3) _The Panamic Sub-region_ extends from the head of the Gulf of
California to Payta in Peru (lat. 5° S.). It is exceedingly rich in
species, about 1500 having been described. The Mollusca are entirely
distinct from those of the Indo-Pacific Region, which, although
extending from Natal to the Sandwich Islands, are unable to pass the
enormous extent of sea which separates the nearest Polynesian island
from the American coast.
On the two sides of the isthmus of Panama there occur certain pairs
of species, which, while specifically distant, are evidently closely
related to one another. Amongst these are, on the Panamic side,
_Purpura speciosa_, _Cypraea cervinetta_, _Cassis abbreviata_, _Natica
Chemnitzii_, and _Strombus gracilior_, corresponding to _Purpura
deltoidea_, _Cypraea exanthema_, _Cassis inflata_, _Natica maroccana_,
and _Strombus pugilis_, on the Caribbean. It is reasonable to conclude
that these “analogous species” are descendants of a stock which was
common to both seas when the isthmus was open (probably not later than
Miocene times), and which have, since the closing of the isthmus,
become modified, some species considerably more than others.
Among the characteristic genera (compare p. 3) are _Conus_,
_Pleurotoma_, _Terebra_, _Murex_, _Purpura_, _Oliva_, _Northia_,
_Cantharus_, _Columbella_, _Anachis_, _Cypraea_, _Strombus_,
_Cerithium_, _Coecum_, _Crepidula_, _Crucibulum_, _Vitrinella_;
_Tellina_, _Semele_, _Tellidora_; and _Arca_.
(4) _The Peruvian Sub-region_ extends from Payta in Peru to about the
latitude of Conception in S. Chili (37° S.), being checked from further
extension southward by the cold Humboldt current, whose force is
distinctly felt as far north as Callao. This cold current thus produces
the same results as the similar current which impinges on S. Africa,
but has even more effect in decisively separating the fauna on the two
sides of the great peninsula, scarcely a single species being common
to the western and eastern coasts of S. America. The characteristics
of the coast-lines themselves contribute to this result. The Chilian
coast is rocky, and descends abruptly to a great depth, while that of
Patagonia and Argentina is sandy and very shallow to a great distance
from land.
The characteristic genera are _Cancellaria_, _Columbella_, _Monoceros_,
_Concholepas_, _Trochita_, _Fissurella_, _Chiton_; _Ceronia_,
_Malletia_, and _Cumingia_. Some of the Californian genera, absent or
poorly represented in the Panamic Sub-region, reappear in Chili, _e.g._
_Scurria_, _Tectura_, and _Chlorostoma_.
(5) _The Magellanic Sub-region_ includes the coast-line and adjacent
islands (with the Falklands) from Conception in S. Chili to about Port
Melo in Eastern Patagonia (lat. 45° S.).
The principal genera (many of which find a habitat on the gigantic
Macrocystis which grows on every rock at low water) are _Euthria_,
_Voluta_ (6 species, one, _V. magellanica_, the largest known)
_Monoceros_, _Photinula_, _Patella_, _Chiton_; _Modiolarca_,
_Malletia_, and _Mulinia_. Several genera characteristic of the Boreal
and Arctic sub-regions recur, _e.g._ _Trophon_, _Admete_, _Margarita_,
_Puncturella_, _Cyamium_, and _Astarte_.
(6) _The Argentinian[390] Sub-region_ extends from about Cape Melo in
Patagonia to the neighbourhood of S. Caterina I. in South Brazil (lat.
28° S.). The sub-region stands in the same relation to the Magellanic,
on the east coast, as the Peruvian sub-region on the west, but, owing
to the influence of the warm Brazil current, which overpowers the
colder water of the Falkland branch of the Cape Horn current, it
reaches a point much farther south.
The Mollusca are not well known. The prevailing genera appear to
be _Oliva_, _Olivancillaria_, _Voluta_, _Bullia_, _Crepidula_;
_Periploma_, and _Lyonsia_.
(7) _The Caribbean Sub-region_ extends from S. Caterina I. in the south
to Florida in the north, and includes the shores of the Gulf of Mexico
and the whole of the West Indies. The influence of the warm Brazil
current (a branch of the South Equatorial) carries the range of the
purely tropical species to a point much farther south than is reached
by the tropical species on the west coast.
The sub-region is very rich in species, especially on the coral reefs
of the Bahamas and N. Cuba, but the exceedingly small tide-fall makes
shore collecting somewhat difficult beyond a certain point. The leading
genera are _Murex_, _Purpura_, _Melongena_, _Latirus_, _Marginella_,
_Strombus_, _Triton_, _Cerithium_, _Littorina_, _Nerita_, _Scalaria_;
_Tellina_, _Strigilla_, _Lucina_, and _Venus_. _Pleurotomaria_, a genus
long regarded as extinct, has been dredged alive off Tobago.
As compared with the tropical fauna of the Old World, that of the New
World is poor in peculiar genera (compare p. 368). The relations of
this sub-region to the West African and the Panamic have been already
dealt with (pp. 367 and 372).
(8) _The Transatlantic Sub-region_ extends from Florida to Cape Cod
(see p. 364). In the north the limits of the sub-region are distinctly
marked, in the south Caribbean species intermingle. Gould and Binney,
in their _Invertebrata of Massachusetts_, enumerate 275 species
(Cephalopoda, 6; Gasteropoda, 159; Scaphopoda, 2; Pelecypoda, 108), of
which 59 (Gasteropoda, 37; Pelecypoda, 22) are British.
Among the characteristic genera are _Urosalpinx_, _Eupleura_, _Fulgur_,
_Ptychatractus_, _Nassa_, _Crepidula_; _Solenomya_, _Mactra_,
_Cypricia_, _Raëta_, _Astarte_, and _Yoldia_. Our common _Littorina
littorea_ appears to have been introduced into Nova Scotian waters in
about 1857, no previous trace of it occurring either in literature or
shell-heaps. Since then it has spread rapidly into the Gulf of St.
Lawrence, and also as far south as Newhaven, and is said to be driving
out the indigenous _L. palliata_ from New England shores.[391] The debt
has been repaid by the introduction into British waters of the American
clam (_Venus mercenaria_ L.), which, according to the _Manchester City
News_ of 23rd March 1889, was first observed in the Humber in 1864, and
has steadily increased up to the present time, when it bids fair to
compete, in those waters, with the familiar _Cardium edule_.
=Characteristics of Abyssal Mollusca.=--Large shells appear to be
rare in the great ocean depths, and are usually very fragile; even
moderately-sized specimens are far from common. The only group in which
species occur larger than the usual size is the Nudibranchs, which are
represented by at least one form larger than an orange.
It would seem that abyssal molluscs are much less active and energetic
than their brethren on the shores. This view is favoured by the
looseness of their tissues, which seem ill adapted for prompt and
vigorous action. The tenacious character of the mud on the ocean floor
must make rapid motion very difficult. The shell itself is usually
fragile and delicate, the upper layers of arragonite being thin as
compared with shallow-water species, which makes the nacreous layer,
when present, appear unusually conspicuous; in many cases the surface
is characterised by a peculiar iridescence or sheen. The colour in
the shell of deep-sea Mollusca is never very pronounced, and is often
absent altogether. Light pink and salmon, pale yellow and brown, are
not uncommon. If the colour is in pattern, it is usually in the form
of necklaces of spots, which sometimes coalesce into bands. With
regard to sculpture, stout knobs and powerfully buttressed varices,
such as occur in the tropical _Murex_ and _Purpura_, are not found in
deep-sea species. But the ornamentation is frequently elaborate, and
the sculpture rich and varied. There is an especial tendency towards
strings of bead-like knobs, revolving striae, and delicate transverse
waves, the sculpture being in many cases of a character which tends to
strengthen the structure of the shell, like the ridges in corrugated
iron.
A remarkable feature in some deep-sea Mollusca is their singular
resemblance, in shape, and particularly in the possession of a strong
green periostracum, to some of our common fresh-water species.
According to Dr. Dall, the cause of this phenomenon is the same in both
cases. The fresh-water Mollusca secrete a strong periostracum, in order
to protect the shell against the corrosive influence of the carbonic
acid gas with which the water is surcharged. The shells of deep-sea
Mollusca, living, as they do, in water probably undisturbed by currents
of any kind, have to protect themselves against the same eroding
influence, and do so in the same way.[392]
Mollusca which live exclusively on algae and other forms of plant life
are almost entirely wanting in the great depths, where vegetation is
probably unknown. The struggle for existence must be much less keen
than in the thickly populated shallows, where vicissitudes of every
kind occur. The absence of rapid motion of water must obliterate many
of those mechanical effects which tend to produce modifying influences
upon the animals affected. In the absence of circumstances tending
to cause variation, in the unbroken monotony of their surroundings,
species must, one would think, preserve a marked uniformity over an
exceedingly wide area of range.
Vegetable food being wanting, those genera which in shallower waters
never taste flesh, are compelled to become carnivorous. Characteristic
of the great depths are very remarkable forms of Trochidae, in whose
stomachs have been found the remains of Corallines and Foraminifera.
According to Dr. Dall, the results of this diet show themselves in the
greatly increased space occupied by the intestine, in the diminution,
as regards size, of the masticatory organs, the teeth and jaws, and
also in the prolongation of the anal end of the intestine into a free
tube, which carries away the excreta in such a way that they do not
foul the water taken into the gills. The amount of nutriment contained
in the bodies of dead Foraminifera is so small that a comparatively
large quantity must be swallowed to keep the vital energies active,
and therefore the amount evacuated must be proportionately larger
also. The abyssal Trochidae, then, and many other genera, sustain
themselves by feeding on the ‘rain’ of dead animal matter which falls
upon the ocean floor, not so much hunting their prey as opening their
mouths and eating whatever happens to fall into them. Genera which are
normally carnivorous would appear to do the same. The Pleurotomidae,
for instance, are a family markedly characteristic of very deep water.
Representatives of the genus which occur in shallower water are known
to secure their prey while in the living state. But, according to
Dr. Dall, a singularly small proportion of deep-sea Mollusca, as
compared with those from the littoral region, show signs of having
been drilled or attacked by other Mollusca. This could hardly be the
case if the Pleurotomidae retained their predatory habits, since they
are more numerous in the great depths than any six other families
taken together. It has already been mentioned (p. 186) that a large
proportion of deep-sea Mollusca are perfectly blind.
Amongst other remarkable forms from the great depths may be mentioned
_Pleurotomaria_, with its singular anal slit (Fig. 269, p. 407)
extending in some cases half way round the last whorl. Three or four
species of this genus, so characteristic of almost all fossiliferous
strata down to the Cambrian, have been obtained in very limited
numbers off the West Indies and Japan. Dentaliidae, especially the
sub-genus _Cadulus_, find a congenial home in the slimy ocean mud.
One of the greatest molluscan treasures procured by the _Challenger_
was _Guivillea alabastrina_ Wats., a magnificent Volute as white as
alabaster, 6½ inches long, which was dredged from 1600 fath. in the
South Atlantic, between Marion Island and the Crozets. Another very
curious form, belonging to the same family, is _Provocator pulcher_
Wats., a shell about half the size of _Guivillea_, of stouter
proportions, and with an angulated and patulous mouth. This shell was
dredged by the _Challenger_ in comparatively shallow water (105–150
fath.) off Kerguelen Island. Among the Trochidae are the fine new
genera _Basilissa_, _Bembix_, and _Gaza_. The exploring voyages of
the American surveying steamer _Blake_, in the Gulf of Mexico and the
Caribbean Sea, have given us the remarkable new forms _Benthobia_
(possibly akin to _Admete_), _Mesorhytis_ (a sub-genus of _Fasciolaria_
hitherto only known from the Cretaceous of North America), and
_Benthodolium_ (possibly = _Oocorys_), a genus akin to _Cassis_.
In his report on the Pelecypoda obtained by the _Challenger_, Mr. E.
A. Smith remarks that as a rule “very deep-water ‘benthal’ species
certainly have a tendency to be without colour and of thin structure,
facts no doubt resulting from the absence of light, the difficulty of
secreting lime, the scarcity of food, and other unfavourable conditions
of existence.” At the same time, he notices that most of the species
obtained belong to genera which, even when occurring in shallow water,
are thin and colourless, _e.g._ _Neaera_, _Lima_, _Cryptodon_, _Abra_,
_Verticordia_, etc. Deep-water species of such genera as have a decided
periostracum (_Malletia_, _Limopsis_, _Leda_, _Nucula_, _Arca_) retain
it with little if any modification. The deep-water Pelecypoda of the
Atlantic and Pacific Oceans present no special features of interest.
The species are few in number, and the genera are not remarkable either
for novelty or peculiarity of form.
The greatest depth at which Pelecypoda have been obtained is 2900 fath.
mid North Pacific (_Callocardia pacifica_ Sm., _Abra profundorum_
Sm.); the greatest depth at which Gasteropoda have been obtained is
2650 fath. South Atlantic (_Stylifer brychius_ Wats.), both by the
_Challenger_. The deepest _Challenger_ Nudibranch came from 2425 fath.,
and the deepest _Chiton_ from 2300 fath. The greatest depth ever
dredged is 4575 fath. off the east coast of Japan.
CHAPTER XIII
CLASS CEPHALOPODA
The Cephalopoda present a complete contrast to the majority of the
Mollusca in habits and in many points of organisation. In their power
of rapid movement and their means of progression, their extreme
ferocity and carnivorous habits, their loss, in so many cases, of a
shell, and in its constitution when present, in the general symmetry of
their parts, in their reproductive and nervous system, they stand in
a position of extreme isolation with nothing to connect them with the
rest of the phylum.
Professor A. E. Verrill has collected many interesting details with
regard to gigantic Cephalopoda occurring on the north-eastern coasts
of America. From these it appears that the tentacular arms of some
species of _Architeuthis_ measure as much as 32, 33, 35, and 42 feet in
length, while the total length, including the body, sometimes exceeds
50 feet. Even off the Irish coast a specimen was once captured whose
tentacular arms were 30 feet long, the mandibles 4 inches across, and
the eyes about 15 inches in diameter.[393] The strength of these giant
Cephalopods, aided as they are by formidable rows of suckers and other
means of securing a grip, is almost incredible. Cases are not uncommon,
in which persons diving or bathing have been attacked, and have with
difficulty made their escape.
Great damage is frequently inflicted by Cephalopoda upon shoals of fish
on British coasts. Off Lybster (Caithness) _Loligo_ and _Ommastrephes_
devour the herring, large numbers of which are cut up and bitten on
the back of the neck by these creatures. On the American coasts the
mackerel fisheries are sometimes entirely spoiled by the immense
schools of squid which infest the Bay of St. Lawrence.[394] When
excited in the pursuit of fish Cephalopoda leap high out of the sea.
Dr. W. H. Rush[395] relates that when about 300 miles off the coast of
Brazil, a swarm of hundreds of decapods flew from the water and landed
on the deck of the ship, which was 12 feet above the surface level, and
they had to go over the hammock nettings to reach it.
[Illustration: FIG. 238.--_Octopus vulgaris_ Lam., Naples: =A=,
At rest; =B=, in motion; _f_, funnel, the arrow showing the
direction of the propelling current of water. (After Merculiano.)]
The common _Octopus vulgaris_ Lam., of British and south European
coasts, inhabits some rocky hole, the approaches to which, like the
den of a fabled giant, are strewn with the bones of his victims. Homer
himself knew how hard it is to drag the polypus out of his hole,
and how the stones cling fast to his suckers. The colour-changes,
which flit across the skin of the _Octopus_, appear, to some extent,
expressive of the different emotions of the animal. They are also
undoubtedly protective, enabling it to assimilate itself in colour to
its environment. Mr. J. Hornell[396] has noticed an _Octopus_, while
crawling over the rock-work in his tank, suddenly change the colour of
the whole right or left side of its body, and of the four arms on the
same side, to a snowy whiteness. They have also been seen to change
colour, as if involuntarily, according to the material on which they
crawl. The nerve-centres which control the chromatophores or pigment
cells, causing them to expand or contract, are found to connect with
the optic ganglia; hence the changes of colour may be regarded as a
reflex result of the creature’s visual perception of its surroundings.
=Order Dibranchiata.=
Cephalopoda with two symmetrical branchiae, funnel completely tubular,
mouth surrounded by 8 or 10 arms furnished with suckers or hooks,
ink-sac and fins usually present, eyes with a lens; shell internal or
absent.
The Dibranchiata are not known from Palaeozoic strata, and first
appear (_Belemnites_, _Belemnoteuthis_) in the Trias. Whether they
are to be regarded as derived from some form of Tetrabranchiata,
_e.g._ _Orthoceras_, or as possessing an independent origin from some
common stock, cannot at present be decided. They attain their highest
development at the present time. The earliest representatives of the
Order (the _Phragmophora_) possessed a shell chambered like that of the
Tetrabranchiata. These chambered Dibranchiates rapidly reached their
maximum in the upper Lias and as rapidly declined, until at the close
of the Cretaceous epoch they were comparatively scarce, only a few
genera (_Beloptera_, _Spirulirostra_) surviving into Tertiary times.
The ordinary Dibranchiate Cephalopod may be regarded as consisting of
two parts--(_a_) the head, in which are situated the organs of sense,
and to which are appended the prehensile organs and the principal
organs of locomotion; (_b_) a trunk or visceral sac, enclosed in
a muscular mantle and containing the respiratory, generative, and
digestive organs. The visceral sac is often strengthened, and the
viscera protected, by an internal non-spiral shell. The ‘arms’ which
surround the mouth are modifications of the molluscan foot (p. 200),
and are either eight or ten in number. In the former case (Octopoda)
the arms, which are termed ‘sessile,’ are all of similar formation, in
the latter (Decapoda), besides the eight sessile arms there are two
much longer ‘tentacular’ arms, which widen at their tips into ‘clubs’
covered with suckers.
Remarks have already been made on the generative organs of Cephalopoda
(p. 136 f.), the branchiae (p. 170), the nervous system (p. 206), the
eye (p. 182), the radula (p. 236), and the ink-sac (p. 241).
One of the most characteristic features of the Dibranchiata are the
_acetabula_, or suckers, with which the arms are furnished. They
are usually disposed on the sessile arms in rows (of which there
are four in most _Sepia_, two in _Octopus_, and one in _Eledone_),
and become more numerous and smaller at the tip of the arm. They
are massed together in large numbers of unequal size on the ‘clubs’
in the Decapoda, particularly in _Loligo_. In most Octopoda their
base is flush with the surface of the arm, but in Decapoda the
acetabula are pedunculate, or raised on short stalks. In Octopoda
again, the acetabula are fleshy throughout, but in the Decapoda they
are strengthened by a corneous rim with a smooth or denticulate
edge (_Ommastrephes_, _Architeuthis_). Many of the acetabula on the
tentacular and sometimes on the sessile arms of the Onychoteuthidae
enclose a powerful hook, which is retractile like the claws of a cat.
In mechanical structure the acetabula consist of a disc with a slightly
swollen margin, from which a series of muscular folds converge
towards the centre of the disc, where a round aperture leads to a
gradually widening cavity. Within this cavity is a sort of button, the
_caruncle_, which can be elevated or depressed like the piston of a
syringe; thus when the sucker is applied the piston is withdrawn and a
vacuum created (Owen).
[Illustration: FIG. 239.--‘Club’ of _Loligo vulgaris_ L., showing
the crowded pedunculate acetabula, × ½.]
[Illustration: FIG. 240.--One of the suckers of _Architeuthis
dux_ Stp., showing the denticulate margin and corneous ring; _p_,
peduncle.]
In many Octopoda the arms are connected by a web (the _umbrella_),
which sometimes extends up the greater part of the arms
(_Cirrhoteuthis_, some _Eledone_), at others occurs only at the
base. The use of the umbrella is perhaps to assist in locomotion, by
alternate contraction and expansion.
A cartilaginous skeleton is well developed, especially in the Decapoda.
In _Sepia_ a cephalic cartilage forms a complete ring round the
oesophagus, the eyes being situated in lateral prolongations of
the same. In front of the cephalic cartilage occurs a piece like an
inverted T, which supports the base of the anterior arms. The
Decapoda have also a ‘nuchal’ cartilage, connecting the head with the
anterior dorsal portion of the mantle, while cartilaginous knobs on the
ventral mantle button into corresponding sockets on the funnel.
=Sub-order I.=--_Octopoda._--Body round or bag-like, generally without
fins, arms eight, suckers fleshy, usually sessile, oviducts paired, no
nidamental glands, shell absent.
[Illustration: FIG. 241.--_Cirrhoteuthis magna_ Hoyle, S.
Atlantic. Two of the left arms and their web have been removed:
_f_, funnel; _fi_, _fi_, fins; _m_, mouth. (After Hoyle, × 1/12.)]
FAM. 1. _Cirrhoteuthidae._--Body with two prominent fins; arms in great
part united by a web; one row of small suckers, with cirrhi on each
side.--Atlantic and Pacific Oceans, deep water (Fig. 241).
FAM. 2. _Amphitretidae._--Body gelatinous, mantle fused with the
funnel in the median line, forming two openings into the branchial
cavity; arms with one row of suckers; umbrella extending more than
two-thirds up the arms.--South Pacific (Fig. 242).
The two pocket-like openings into the branchial cavity are unique among
Cephalopoda (Hoyle).
[Illustration: FIG. 242.--_Amphitretus pelagicus_ Hoyle, off
Kermadec Is.: _e_, eyes; _f_, funnel; _p_, right mantle-pocket.
(After Hoyle.)]
FAM. 3. _Argonautidae._--Female furnished with a symmetrical,
unilocular shell, spiral in one plane, secreted by thin terminal
expansions (the _vela_) of the two dorsal arms, no attachment muscle;
suckers in two rows, pedunculate; male very small, without veligerous
arms or shell.--All warm seas (Fig. 243). Pliocene----.
The shell consists of three layers, the two external being prismatic,
the middle fibrous. Its secretion by the arms and not by the mantle
edge is unique, and shows that it is not homologous with the ordinary
molluscan shell.
[Illustration: FIG. 243.--_Argonauta argo_ L., the position
assumed by a specimen kept in captivity, the arrow showing
the direction of movement: _f_, funnel; _m_, mouth, with jaws
projecting; _sh_, shell, with arms as seen through it; _wa_,
webbed arm clasping shell. (After Lacaze-Duthiers.)]
The great controversy on the _Argonauta_, which once raged with so
much fierceness, is now matter of ancient history. It seems scarcely
credible that between fifty and sixty years ago, two of the leading
zoologists of the day, Mr. Gray and M. de Blainville maintained that
the animal which inhabits the Argonaut shell is a parasite, without any
means of depositing or forming a shell of its own, but which possesses
itself of the Argonaut shell, either by expelling or succeeding the
original inhabitant, a supposed nucleo-branchiate (Heteropod) mollusc
akin to _Carinaria_. The final blow to this strange hypothesis--which
was urged by the most ingenious series of arguments--was given by
Professor Owen, who in 1839 brought before the Zoological Society
of London the admirable observations of Madame Jeannette Power, who
made a continuous study of a number of specimens of _Argonauta_ in
her vivarium at Messina. The result of these observations tended to
show that the young _Argonauta_ when first excluded from the egg is
naked, but that in ten or twelve days the shell begins to form, that
the principal agents in the deposition of shell are the two velated
or web-like arms; and that portions of the shell, if broken away, are
repaired by a deposition of calcareous matter.[397]
FAM. 4. _Philonexidae._--Mantle supported by two ridges placed on
the funnel; large ‘aquiferous’ pores (supposed to introduce water
into the tissues) near the head or funnel; suckers in two rows,
pedunculate.--Atlantic and Mediterranean.
Genera: _Ocythoe_, arms of unequal size, no intervening membrane, third
arm on the right hectocotylised (see Fig. 51, p. 138), two aquiferous
pores at the base of the siphon; male very small; _Tremoctopus_, two
aquiferous pores between the eyes, two on the ventral side of the head.
FAM. 5. _Alloposidae._--Mantle edge united to the head by three
commissures; arms extensively webbed, acetabula sessile. Hectocotylised
arm developed in a cavity in front of the right eye.--N. Atlantic.
FAM. 6. _Octopodidae._--Head very large, arms elongated, similar,
more or less webbed, acetabula usually in two rows, sessile; mantle
supported by fleshy bands, no cephalic aquiferous pores.
In _Octopus_ proper the web is usually confined to the lower part of
the arms; Fischer separates off as _Pteroctopus_ a form in which it
reaches almost to their extremity. The third right arm (Fig. 52, p.
140) is hectocotylised, the modified extremity being, according to
Hoyle, sometimes minute, sometimes spoon-shaped, with a tendency to
transverse ridges, rarely slender and very long. The relative length
of the pairs of arms varies in different species. Two cartilaginous
stylets, imbedded in the dorsal mantle, are said by Owen to represent
the shell.
Other genera; _Pinnoctopus_, body furnished with broad lateral wings
which meet at the posterior end; _Cistopus_, a large web prolonged
along the sides of the arms, fitted with oval aquiferous pouches, with
pores at their base, between each pair of arms; _Eledone_ (Fig. 244),
one row of acetabula; _Tritaxeopus_, _Iapetella_.
=Sub-order II.=--_Decapoda._--Body oblong, mouth surrounded by
four pairs of sessile and one pair of tentacular arms, the latter
terminated by a ‘club’; acetabula pedunculate and furnished with a
corneous margin; mantle margin locked to the base of the funnel by a
cartilaginous apparatus; head and anterior part of body furnished with
aquiferous pores; fins present; mandibles corneous; oviduct single,
large nidamental glands in the female; shell internal.
[Illustration: FIG. 244.--_Eledone Aldrovandi_ Delle Chiaje,
Naples, from ventral side, × ½.]
The tentacular arms, which are the principal external feature of the
Decapoda, are not derived from the same muscular ring as the sessile
arms, but arise from the cephalic cartilage, and emerge between the
third and fourth arm on each side. In _Sepia_ they can be entirely
retracted into a kind of pocket behind the eyes, while in _Loligo_ they
are simply folded over one another. In _Chiroteuthis_ the arms are six
times as long as the body, and the clubs have four rows of denticulate
suckers.
The anterior ventral[398] portion of the mantle is furnished with a
singular contrivance for locking it to the funnel, and so rendering the
whole animal more capable of resisting the impact of any force. This
contrivance generally consists of a series of ridges or buttons which
fit into grooves or button-holes, the ridges being on the interior face
of the mantle and the corresponding grooves on the funnel, or _vice
versâ_. The ‘resisting apparatus’ is most elaborate in the pelagic
genera, and least so in the more sluggish littoral forms. A similar,
but not so complex, arrangement occurs also in the Octopoda.
The different forms of the shell appear to indicate successive stages
in a regular course of development. We have in _Spirula_ (Fig. 247)
a chambered shell of the Tetrabranchiate type, but of considerably
diminished size, which has ceased to contain the animal in its last
chamber, and has become almost entirely enveloped in reflected folds
of the mantle. These folds gradually concresce to form a definite
shell-sac, by the walls of which are secreted additional laminae of
calcareous shell-substance. These laminae invest the original shell,
which gradually (_Spirulirostra_, _Belosepia_) loses the spiral form
and becomes straight, eventually disappearing, while the calcareous
laminae alone remain (_Sepia_). These in their turn disappear, leaving
only the plate or ‘pen’ upon which they were deposited (_Loligo_),
which itself also, with the shell-sac, finally disappears, surviving
only in the early stages of _Octopus_ (Lankester).
The Decapoda are divided, according to the character of the shell, into
_Phragmophora_, _Sepiophora_, and _Chondrophora_.[399]
[Illustration: FIG. 245.--‘Club’ of _Onychoteuthis_ sp., showing
the hooks and clusters of fixing cushions and acetabula below
them, × ½.]
A. PHRAGMOPHORA.--Arms furnished with hooks or acetabula; shell
consisting of a _phragmocone_ or chambered sac enclosed in a thin wall
(the _conotheca_), septa pierced by a siphuncle near the ventral margin
(in _Spirula_ alone this chambered sac forms the whole of the shell).
The apex of the cone lies towards the posterior end of the body, and
is usually enveloped in a calcareous _guard_ or _rostrum_. Beyond the
anterior end of the rostrum the conotheca is extended forward dorsally
by a _pro-ostracum_ or anterior shell, which may be shelly or horny,
and corresponds to the _gladius_ of the Chondrophora. The rostrum
consists of calcareous fibres arranged perpendicularly to the planes
of the laminae of growth, and radiating from an axis, the so-called
_apical line_, which extends from the extremity of the phragmocone to
that of the rostrum. _Distribution_, see p. 380.
FAM. 1. _Spirulidae._--Arms with acetabula, shell a loose spiral,
without rostrum or pro-ostracum, partially external, enclosed in two
lobes of the mantle (Figs. 247 and 248).
The single species of the single genus (_S. Peronii_ Lam. = _laevis_
Gray) has not yet been thoroughly investigated, although the shell
occurs in thousands on many tropical beaches, and is sometimes drifted
on our own shores. The animal appears to have the power of adhesion
to the rocks by means of a terminal sucker or pore. The protoconch
is present, and contains a prosiphon, which does not connect with
the siphuncle. The septal necks are continuous, not broken as in
_Nautilus_. The siphuncle is on the ventral margin of the shell, the
last whorl of which projects slightly on the dorsal and ventral sides,
but is even there covered by a thin fold of the mantle. The retractor
muscles of the funnel and of the head find their _point d’appui_ on the
shell, the last chamber of which contains the posterior part of the
liver, with which the membranous siphuncle is connected.
FAM. 2. _Belemnitidae._--Arms hooked as in _Onychoteuthis_, fins large;
phragmocone straight, initial chamber globular, larger than the second,
rostrum often very long, investing the phragmocone, pro-ostracum
sword- or leaf-shaped, rounded in front, seldom preserved, ink-sac
present.--Lower Lias to Cretaceous.
[Illustration: FIG. 246.--_Sepia officinalis_ L., with mantle cut
away to show position of internal shell, × ½. (The ends of the
tentacular arms are cut off.)]
The Belemnitidae are believed to have been gregarious, and to have
lived in shallow water on a muddy bottom. Specimens are sometimes found
in which even the ink-sac can be recognised _in situ_. The relative
proportions of rostrum and phragmocone vary greatly in different
groups, the rostrum being in some cases two feet long, in others only
just enclosing the phragmocone. As a rule the rostrum is the only
portion which has been preserved.
FAM. 3. _Belosepiidae._--Phragmocone short, slightly curved, chambers
small, placed at the posterior end of a sepion, rostrum solid,
obtuse.--Eocene (Paris, Bracklesham, etc.).
_Fam. 4._ _Belopteridae._--Sepion not known; phragmocone curved,
siphuncle on the ventral margin, rostrum well developed, pointed.
Principal genus, _Spirulirostra_.--Miocene of Turin.
These two families, with their small, curved phragmocone and (in the
case of the Belosepiidae) large sepion, are clearly intermediate
between the Phragmophora and Sepiophora. Some authorities place them
with the latter group.
[Illustration: FIG. 247.--Shell of _Spirula Peronii_ Lam.
=A=, Cutside view; =B=, showing last chamber and position of
siphuncle; =C=, in section, showing the septa and course of
siphuncle; =D=, shell broken to show the convexity of the inner
side of the septa; =E=, portion of a septal neck.]
[Illustration: FIG. 248.--_Spirula Peronii_ Lam.: _d_, terminal
sucker; _f_, funnel; _s_{1}_, _s_{2}_, projecting portions of
shell, the internal part of which is dotted in. (From Owen and A.
Adams combined.)]
B. SEPIOPHORA.--Shell internal, consisting usually of (_a_) an anterior
cancellated portion, (_b_) a posterior laminated portion, the laminae
enclosing air. It terminates in a very rudimentary phragmocone and a
rostrum, but there is no siphuncle.
FAM. _Sepiidae._--Eyes with cornea complete, body oval, fins narrow,
lateral, as long as the body, generally united behind; sessile arms
short, tentacular arms long, acetabula generally in four rows,
fourth left arm in the male hectocotylised near the base (Fig.
249).--World-wide.
The sepion or ‘cuttle-bone’ runs the whole length and width of the
body. In _Sepia_ it is very thick in front, while the posterior ventral
end is concave and terminated by a prominent spine, the _rostrum_ or
_mucro_ which points downwards. The whole shell is surrounded by a thin
chitinous margin, which forms a lateral expansion. Other genera are
_Sepiella_, _Hemisepius_, and _Trachyteuthis_ (fossil only).
C. CHONDROPHORA.--Shell (_gladius_ or _pen_) long, chitinous.
(_a_) _Myopsidae:[400] cornea entire, species mostly sub-littoral._
FAM. 1. _Sepiolidae._--Fins large, dorso-lateral; tentacular arms
retractile; two first dorsal arms in the male hectocotylised; gladius
narrow, half as long as the body.--World-wide.
Principal genera: _Sepiola_, dorsal mantle connected with the head by a
broad cervical band, ventral mantle with the funnel by a ridge fitting
into a groove; _Rossia_, dorsal mantle supported by a ridge, arms with
never more than four rows of acetabula; _Inioteuthis_, _Stoloteuthis_,
_Nectoteuthis_, and _Promachoteuthis_.
FAM. 2. _Sepiadariidae._--Fins not as long as the body, mantle
united to the head on the dorsal side, fourth left arm in the
male hectocotylised; no gladius. Principal genera, _Sepiadarium_,
_Sepioloidea_.--Chiefly Pacific Ocean.
[Illustration: FIG. 249.--Hectocotylised arm (_h.a._) of _Sepia
officinalis_ L., shown in contrast to one of the ordinary sessile
arms; _m_, mouth; _p_, pocket into which the tentacular arm is
retracted.]
FAM. 3. _Idiosepiidae._--Fins very small, terminal; fourth pair of arms
in the male hectocotylised, bare of suckers.
The only genus, _Idiosepion_, with a single species (_I. pygmaeum_
Stp.) is from the Indian Ocean, and is the smallest known Cephalopod,
measuring only about 15 mm. in length.
FAM. 4. _Loliginidae._--Body rather long, fins varying in size,
tentacular arms partially retractile, gladius as long as the back,
pointed in front, shaft keeled on the ventral side.--World-wide.
_Loligo_ proper has a pointed body with triangular posterior fins
united behind; sessile arms with two rows of acetabula, tentacular
arms with four; fourth left arm hectocotylised at the tip; funnel
attached to the head. Other genera are _Loliguncula_, _Sepioteuthis_,
and _Loliolus_. _Belemnosepia_, _Beloteuthis_, _Leptoteuthis_, and
_Phylloteuthis_ are fossil genera only, differing in the shape of the
gladius.
(_b_) _Oigopsidae: cornea more or less open; species pelagic._
FAM. 5. _Ommastrephidae._--Body cylindrical, fins generally terminal,
united together, regularly rhomboidal, sessile arms with varying number
of rows of acetabula, mantle connexions elaborate; gladius horny,
narrow lanceolate, with a hollow cone at the posterior end.--World-wide.
[Illustration: FIG. 250.--_Architeuthis princeps_, Verr., E.
America: _f_, Right fin; _fu_, funnel; _f.c_, fixing cushions and
acetabula on the tentacular arms (_t_, _t_). (After Verrill, ×
1/60.)]
_Ommastrephes_ proper has a natatory web on the sessile arms; the wrist
of each club has a series of acetabula with corresponding cushions on
the other wrist. In _Thysanoteuthis_ (often made a separate family)
the sessile arms have two rows of cirrhi, with lateral expansions of
the skin; fins as long as the body. In _Architeuthis_, to which belong
the largest Cephalopoda known, the fins together are shaped like a
broad arrow-head; acetabula of sessile arms strongly denticulate;
tentacular arms very long, with equidistant pairs of acetabula and
fixing cushions throughout their entire length, and a group of the same
at the base of the club. The acetabula and cushions correspond on the
opposing tentacles, and enable them to pull together. Other genera are
_Dosidicus_, _Todarodes_, _Illex_, _Bathyteuthis_ and _Mastigoteuthis_.
FAM. 6. _Onychoteuthidae._--Body cylindrical, fins terminal or lateral,
mantle-locking apparatus elaborate, tentacular arms very long, sessile
or tentacular arms furnished with retractile hooks, gladius lanceolate,
with a terminal cone.--World-wide.
The prehensile apparatus of Cephalopoda reaches its maximum of power
and singularity in this family. In _Onychia_, _Onychoteuthis_
and _Ancistroteuthis_, the sessile arms have acetabula only, in
_Gonatus_ and _Abralia_ they have hooks as well, while in _Verania_,
_Ancistrochirus_ and _Enoploteuthis_, the sessile arms have hooks only.
The number of rows of hooks or acetabula varies with the different
genera.
FAM. 7. _Chiroteuthidae._--Head nearly as large as the body; fins
terminal, tentacular arms very long, sessile arms slightly webbed,
acetabula denticulated; mantle-supports consisting of cartilaginous
ridges on the mantle, which fit into corresponding depressions on the
funnel, gladius expanded at each end.--Atlantic Ocean.
The six dorsal arms in _Histioteuthis_ are united by a broad web,
while in _Histiopsis_ the web only reaches half way up the arm. In
_Chiroteuthis_ the tentacular arms have scattered sessile suckers
throughout their whole length, and four rows of very long pedunculate
suckers on the clubs.
FAM. 8. _Cranchiidae._--Head small, body rounded, barrel-shaped, fins
terminal, eyes often very large, sessile arms short, tentacular arms
long, thread-like.--World-wide.
_Cranchia_ proper has the tentacular clubs finned, with eight rows of
suckers, body sometimes covered with warty tubercles. _Loligopsis_ has
a very attenuated body, with fins terminally united; some species are
spotted with colour, or have rows of tubercles on the ventral side.
_Taonius_ (Fig. 251) is doubtfully distinct from _Loligopsis_.
[Illustration: FIG. 251.--_Taonius hyperboreus_ Stp., N.
Atlantic: _e_, _e_, eyes; _f_, _f_, fins; _t_, _t_, tentacular
arms. (After Hoyle, × ¼.)]
=Order Tetrabranchiata=
Cephalopoda with four branchiae and four kidneys; animal inhabiting the
last chamber of an external multilocular shell; funnel consisting of
two separate lobes; tentacles numerous, without suckers or hooks; no
ink-sac.
The shell consists of two layers, the outer being porcellanous, and
the inner, as well as the walls of the chambers or _septa_, nacreous.
The septa vary greatly in shape. In most of the Nautiloidea they are
regularly curved, as in _Nautilus_, or straight, as in _Orthoceras_,
but in the Ammonoidea they are often exceedingly complex. The edge of
the septum, where it unites with the shell-wall, is called the suture,
and the sutural line, which is not seen until the porcellanous layer is
removed, varies in shape with the septum.
[Illustration: FIG. 252.--_Nautilus pompilius_ L., in section,
showing the septa (_s_, _s_), the septal necks (_s.n_, _s.n_),
the siphuncle dotted in (_si_), and the large body chamber
(_ch_).]
The septa are traversed by a membranous tube known as the _siphuncle_,
which in _Nautilus_ is said by Owen to connect ultimately with the
pericardium. The _septal necks_, or short tubular prolongations of the
septa where they are perforated by the siphuncle, are in the great
majority of the Nautiloidea directed backwards (Fig. 252), _i.e._,
they project from the front wall of each chamber, while in nearly all
Ammonoidea they are directed forwards. When the siphuncle is narrow,
as in the Ammonoidea, it is simple, but when wide, as in many of the
Nautiloidea, its walls are often thickened by the deposition of
masses of calcareous matter, or by rings and radiating lamellae of
the same material. In position, the siphuncle is sometimes central,
sometimes sub-central, sometimes (Ammonoidea) marginal. In some cases
its position is believed to change during the growth of the individual.
The precise object served by the siphuncle is at present unknown. Some
hold that it preserves the vitality of the unoccupied chambers, by
connecting them with the soft parts of the animal; others have regarded
it as a means for lightening the shell by the passage of some gas into
the chambers.
[Illustration: FIG. 253.--_Ammonites_ (_Cadoceras_) _sublaevis_
Sowb., Kellaway’s Rock, showing the marginal position of the
siphuncle (_si_).]
The initial chamber in Nautiloidea consists of an obtuse incurved cone,
marked on the outer surface of its posterior wall by a small scar known
as the _cicatrix_, which may be slit-like, round, oval, or cruciform
in shape. It has been held that the cicatrix originally communicated
with the protoconch or larval shell, which probably dropped off as
development proceeded. In the Ammonoidea, on the other hand, there
is no cicatrix, and the initial chamber probably represents the
protoconch, as seen in the nucleus of many Gasteropoda.
=Sub-order 1.= _Nautiloidea._--Shell straight, bent, or coiled,
aperture simple or contracted; siphuncle often narrowed by internal
deposits, position variable; septal necks short, usually directed
backwards; septa concave towards the aperture; initial chamber conical,
with a cicatrix on the posterior wall.
The Nautiloidea, of which _Nautilus_ is the sole living representative,
date back to the Cambrian epoch, and attain their maximum in the
Silurian and Devonian. At the close of the Palaeozoic era, every
family, with the sole exceptions of the _Orthoceratidae_ and
_Nautilidae_, appears to have become extinct. The former disappear with
the Trias, and after the lapse of the whole Secondary era, _Aturia_, a
form closely related to _Nautilus_, makes its appearance.
(_a_) _Retrosiphonata_: septal necks directed _backwards_.
FAM. 1. _Orthoceratidae._[401]--Shell straight or slightly curved,
aperture simple, body-chamber large; siphuncle cylindrical, position
variable. Single genus, _Orthoceras_ (Fig. 254). Cambrian to Trias.
FAM. 2. _Endoceratidae._--Shell straight, siphuncle wide, marginal,
septal necks produced into tubes fitting into one another. Principal
genera: _Endoceras_ (specimens of which occur six feet long), and
_Piloceras_--Ordovician.
FAM. 3. _Actinoceratidae._--Shell straight or slightly curved,
siphuncle wide, contracted at the septa by obstruction-rings.
Principal genera: _Actinoceras_, _Discosorus_, _Huronia_,
_Sactoceras_.--Ordovician to Carboniferous.
FAM. 4. _Gomphoceratidae._--Shell globular, straight or considerably
curved, aperture narrowed, T-shaped, body-chamber large, siphuncle
variable in position. The aperture is in some cases so narrow
that probably only the arms could be protruded. Principal genus,
_Gomphoceras_ (Fig. 255).--Silurian.
FAM. 5. _Ascoceratidae._--Shell sac-like or flask-shaped, apex
truncated, unknown, body-chamber occupying nearly the whole of
the shell on the ventral side, contracting at the aperture, last
few septa coalescing on the dorsal side and encroaching upon the
body-chamber. The young form has a symmetrical shell like _Orthoceras_,
attached to the sac-like shell above described; as growth proceeds
the former portion is thrown off. Principal genera: _Ascoceras_,
_Glossoceras_.--Ordovician and Silurian.
[Illustration: FIG. 254.--=A=, Section of _Orthoceras_, showing
the septa (_s_, _s_), and siphuncle (_si_, _si_); =B=, portion of
the exterior of _Orthoceras annulatum_ Sowb., × ½. (Woodwardian
Museum, Cambridge.)]
FAM. 6. _Poterioceratidae._--Shell fusiform, contracted at both ends,
aperture simple, siphuncle variable in position, inflated between the
septa. The form generally resembles _Gomphoceras_, except for the
simple aperture and fusiform shape.--Ordovician to Carboniferous.
FAM. 7. _Cyrtoceratidae._--Shell conical or sub-cylindrical, slightly
curved, body-chamber large, siphuncle variable in position. Single
genus, _Cyrtoceras_.--Cambrian to Carboniferous.
FAM. 8. _Lituitidae._--Shell coiled in a flat, sometimes loose spiral,
last whorl straight, containing the body-chamber, often greatly
prolonged. Principal genera: _Lituites_, _Ophidioceras_.--Ordovician
and Silurian.
FAM. 9. _Trochoceratidae._--Shell helicoid, with seldom more than two
whorls, dextral or sinistral, last whorl sometimes partly uncoiled.
Principal genera: _Trochoceras_, _Adelphoceras_.--Ordovician to
Devonian.
FAM. 10. _Nautilidae._--Shell with few whorls, more or less
overlapping, septa simple, siphuncle central or sub-central, aperture
not contracted.
The ‘tentacles’ are about 90 in number, and consist of four groups each
of 12 or 13 labial tentacles surrounding the mouth, two groups each of
17 larger (brachial) tentacles on each side of the head, two thicker
tentacles which combine to form the ‘hood,’ and two small tentacles
on each side of the eye. When the animal swims, the tentacles are
extended radially from the head, somewhat like those of a sea-anemone.
The direction of the many pairs of tentacles at constant but different
angles from the head, is the most striking feature in the living
_Nautilus_, and accounts for its being described, when seen on the
surface, as ‘a shell with something like a cauliflower sticking out
of it.’[402] The funnel is not a complete tube, but is formed by the
overlapping of the margins of two thin fleshy lobes (which are probably
morphologically epipodia), so that when the two lobes are parted, a
broad canal appears, leading to the branchial cavity. The head is
conical, and the mouth and its appendages can be retracted into a sort
of sheath, over which fits the ‘hood.’
[Illustration: FIG. 255.--=A=, _Gomphoceras ellipticum_ M’Coy,
Silurian: =B=, aperture (_ap_) of same; _s_, _s_, septa; _si_,
position of siphuncle. (After Blake.)]
Other genera are _Trocholites_, _Gyroceras_, _Hercoceras_, _Discites_,
_Aturia_.--Ordovician to present time.
FAM. 11. _Bactritidae._--Shell straight, conical, siphuncle small,
marginal, septal necks long, funnel-shaped, sutures undulating, with
a sinus corresponding to the siphuncle. This family, from the form of
its sutures, appears to constitute a passage to the Ammonoidea. Single
genus, _Bactrites_.--Silurian and Devonian.
(_b_) _Prosiphonata._--Septal necks directed _forwards_.
The two genera are _Bathmoceras_ (Ordovician), shell straight, conical
always truncated, siphon marginal; and _Nothoceras_ (Silurian), shell
nautiloid with simple sutures.
=Sub-order 2.= _Ammonoidea._--Shell multiform, straight, curved, flat
spiral, or turreted, sutural line more or less complex, siphuncle
simple.
Some authorities hold that the members of this great sub-order, now
totally extinct, belong to the Dibranchiata, on the ground that
the protoconch resembles that of _Spirula_ rather than that of the
Nautiloidea. Others again regard the Ammonoidea as a third, and
distinct Order of Cephalopoda. Their distribution extends from the
Silurian to (possibly) the early Tertiary. No trace has ever been
found of an ink-sac, mandible, or hooks on the arms; the shell was
undoubtedly external.
[Illustration: FIG. 256.--Diagram of the sutures of Ammonites:
=A=, an elaborate suture (_Phylloceras_); =B=, a simple suture
(_Ceratites_); _s.s_, siphonal, _s.v_, ventral, _s.l_, first
lateral, _s.l´_, second lateral saddles; _s.a_, _s.a_, auxiliary
saddles; _l.v_, ventral, _l_, first lateral, _l´_, second lateral
lobe; _l.a_, _l.a_, auxiliary lobes. The arrow points _towards_
the aperture. (From Woodward.) Compare Fig. 258.]
The sutural line, which indicates the septa, and is generally
concealed beneath the outer layer of shell, consists of a number of
_lobes_ or depressions, the concave part of which is directed towards
the aperture. Between these lobes lie corresponding elevations, or
_saddles_, the convex part of which is directed towards the aperture.
There are six principal lobes (Fig. 256): the _siphonal_ or _ventral_,
which is traversed by the siphuncle, the _dorsal_, and a superior and
inferior lateral on each side; smaller auxiliary lobes may succeed
these latter. The adjacent saddles have received corresponding
names. As a rule the sutural line is very complex, but in some cases
(_Goniatites_, _Lobites_) it is simple (Fig. 258, A). The first saddle
of a large number of genera serves as a means of classification,
according as it is broad or narrow. Some authorities reverse the terms
ventral and dorsal, as applied above. It is probable, however, that
the position of the animal of _Ammonites_ in its shell resembled that
of _Nautilus_. The siphuncle is dorsal (internal) in _Clymenia_ only,
ventral (external) in all other genera.
The _aptychus_ of Ammonoidea is a corneous or calcareous valve-like
body, generally formed of two symmetrical parts (Fig. 257). It has been
regarded by some as the covering of the nidamental gland, and hence as
occurring only in the female, by others, with more probability, as an
operculum, covering or imbedded in a hood formed, as in _Nautilus_,
of modified arms. Sometimes the Aptychus is in a single piece
(_Anaptychus_), sometimes the two pieces are united on the median line
(_Synaptychus_).
[Illustration: FIG. 257.--Aptychus of Ammonite (_Trigonellites
latus_). Kimmeridge Clay, Ely. × ½.]
The Ammonoidea are thus classified by Dr. P. Fischer:--
(_a_) Retrosiphonata _Goniatitidae_.
{ First saddle, { _Arcestidae_, _Tropitidae_,
{ No Aptychus or { wide { _Ceratitidae_, _Clydonitidae_.
{ Anaptychus {
{ corneous, { { _Pinacoceratidae_, _Amaltheidae_,
(_b_) Prosiphonata { single { First saddle, { _Ammonitidae_,
{ { narrow { _Lytoceratidae_.
{
{ Aptychus calcareous, valves { _Harpoceratidae_, _Stephanoceratidae_.
{ double or united
(_a_) _Retrosiphonata._ FAM. 1. _Goniatitidae._--Shell nautiloid,
whorls sometimes disjoined, siphuncle ventral or dorsal, sutures
simple. Principal genera: _Clymenia_, _Goniatites_ (Fig. 258,
A).--Devonian to Carboniferous.
(_b_) _Prosiphonata._ FAM. 2. _Arcestidae._--Shell globular, smooth
or striated and rayed, body-chamber very long, aperture often with
a projecting hood, umbilicus closed by a callosity, lobes numerous,
foliaceous, aptychus present. Principal genera: _Arcestes_,
_Lobites_.--Principally Trias.
FAM. 3. _Tropitidae._--Differs from Arcestidae mainly in the more
highly ornamented surface, which is decorated with ribs which become
granular at the periphery. Principal genus, _Tropites_.--Trias and Lias.
FAM. 4. _Ceratitidae._--Shell ribbed and tuberculated, body-chamber
short, lobes denticulated, saddles simple. Principal genera:
_Ceratites_ (Fig. 258, B), _Trachyceras_.--Principally Trias.
FAM. 5. _Clydonitidae._--Shell variable in form, body-chamber short,
sutural line undulated, simple. Principal genera: _Clydonites_,
_Choristoceras_, _Rhabdoceras_, _Cochloceras_.--Trias.
FAM. 6. _Pinacoceratidae._--Shell discoidal, usually smooth,
body-chamber short, sutural line very complex, lobes numerous.
Principal genera: _Pinacoceras_, _Sageceras_.--Carboniferous to Trias.
FAM. 7. _Amaltheidae._--Shell broad, keeled, last whorl concealing most
of the spire, sutures with auxiliary lobes, incised.--Principal genera:
_Amaltheus_, _Schloenbacia_, _Sphenodiscus_.--Trias, Cretaceous.
[Illustration: FIG. 258.--Various forms of Ammonoidea: =A=,
_Goniatites crenistria_ J. Phil., Carb. Limestone; =B=,
_Ceratites nodosus_ de Hann., Muschelkalk; =C=, _Ammonites_
(_Parkinsonia_) _Parkinsoni_ Sowb., Inf. Oolite; =D=,
_Phylloceras helerophyllum_ Sowb., Upper Lias; _s_, _s_, sutural
lines.]
FAM. 8. _Ammonitidae._--Body-chamber long, whorls narrow,
uncovered, more or less ribbed, aperture simple, sutural line
normal, aptychus single, corneous. Principal genera: _Ammonites_,
_Aegoceras_.--Principally Lias.
FAM. 9. _Lytoceratidae._--Shell discoidal, body-chamber short, aperture
simple, no aptychus. Principal genera: _Lytoceras_, _Phylloceras_ (Fig.
258, D).--Trias to Cretaceous.
FAM. 10. _Harpoceratidae._--Shell discoidal, compressed, margin
keeled, surface with straight or arched ribs, aperture with lateral
projections, suture with accessory lobes, aptychus in two pieces.
Principal genera: _Harpoceras_, _Oppelia_, _Lissoceras_.--Jurassic to
Cretaceous.
[Illustration: FIG. 259.--=A=, _Turrilites catenulatus_ d’Orb,
Gault; =B=, _Macroscaphites Iranii_ d’Orb, Upper Neocomian. (From
Zittel.)]
FAM. 11. _Stephanoceratidae._--Shell discoidal, helicoid or straight,
whorls sometimes disunited, surface often with bifurcating ribs, which
are tubercled, aperture often with lateral projections, sutural line
incised, aptychus in two pieces, sometimes united.
In the discoidal group, _Stephanoceras_ is strongly ribbed,
tubercled at the point of bifurcation, _Cosmoceras_ has long lateral
projections of the aperture when young, _Perisphinctes_ has a large
body-chamber and numerous smooth ribs. Other genera are _Acanthoceras_,
_Peltoceras_, _Aspidoceras_, and _Hoplites_. Among the loosely
whorled genera, _Scaphites_ (Fig. 260, A) has the last whorl produced
and bent back again in horse-shoe form, while the early whorls are
concealed; _Hamites_, _Hamulina_, and _Ptychoceras_ have a shell
shaped like a single or double hook, the sides of which may or may not
be united; _Crioceras_ (Fig. 260, B) in form of whorls resembles a
_Spirula_, _Ancyloceras_ a _Scaphites_ with the first whorls disunited.
_Macroscaphites_ (Fig. 259, B) is similar, but with the first whorls
united and not concealed. _Turrilites_ (Fig. 259, A) is turreted
and sinistral, while _Baculites_ is quite straight, with a long
body-chamber.
[Illustration: FIG. 260.--=A=, _Scaphites aequalis_ Sowb.,
Cretaceous; =B=, _Crioceras bifurcatum_ Quenst., Cretaceous.
(From Zittel.)]
CHAPTER XIV
CLASS GASTEROPODA--AMPHINEURA AND PROSOBRANCHIATA
=Order I. Amphineura=
Bilaterally symmetrical Mollusca, anus at the terminal end of the body,
dorsal tegument more or less furnished with spicules.
=Sub-order 1.= =Polyplacophora= (Chitons).--Foot co-extensive with
ventral surface of the body, dorsum with eight transverse plates,
articulated (except in _Chitonellus_), a row of ctenidia on each side
between the mantle and the foot. Silurian ----.
The Chitons are found in all parts of the world, ranging in size from
a length of about half an inch to six inches or more in the giant
_Cryptochiton_. Although in the main sub-littoral, they occur at very
great depths; the _Challenger_ dredged _Leptochiton benthus_ Hadd. at
2300 fathoms. _Chiton Polii_ exceptionally occurs at Malta--_teste_
MacAndrew--above sea margin, but within reach of the ripple. As a
rule, the Chitons live in concealment, on the under surface of stones
or in deep and narrow fissures in the rocks. When the stone to which
they are attached is turned over, they crawl slowly to the side which
is not exposed, as if disliking the light. An undescribed species,
however, which I took at Panama, crawled quite as fast as an ordinary
snail. _Chiton fulvus_ Wood, apparently is accustomed to crawl with
some rapidity. MacAndrew took it in abundance on his anchor chain in
Vigo Bay every time his yacht was got under weigh. He also found it
crawling in sand on the shore, to which habit is no doubt due its
extreme cleanness and freedom from the foreign growths which are
so characteristic of many of the species. When detached a _Chiton_
contracts the muscles of the whole body, and rolls up into a ball like
a wood-louse.
[Illustration: FIG. 261.--Valves of a _Chiton_ separated to
show the various parts (anterior valve uppermost): _a_, _a_,
articulamentum; _b_, beak; _j_, jugum; _pl_, _pl_, pleura; _t_,
_t_, tegmentum.]
[Illustration: FIG. 262.--Valves of _Chitonellus_ separated out
(anterior valve uppermost): _a_, _a_, articulamentum; _t_, _t_,
tegmentum. × 2.]
The _Polyplacophora_ are characterised, _externally_, by their usually
articulated shell of eight _plates_ or _valves_, which is surrounded
and partly kept in position by a muscular _girdle_. These plates
overlap like tiles on a roof in such a way that the posterior edge of
the first, cephalic, or anterior valve projects over the anterior edge
of the succeeding valve, which in its turn overlaps the next, and so on
throughout. Seven-valved monstrosities very rarely occur.
A certain portion of each valve is covered either by the girdle or
by the valve next anterior to it. This portion, which is whitish in
colour and non-porous in structure, forms part of an inner layer which
underlies the rest of the substance of the valve, and is called the
_articulamentum_. The external portion of the valves, or _tegmentum_,
is generally more or less sculptured, and is largely composed of
chitin, impregnated with salts of lime, thus answering more to a
cuticle than to a shell proper. It is very porous, being pierced by
a quantity of minute holes of two sizes, known as _megalopores_ and
_micropores_, which are connected together by minute canals containing
what is probably fibrous or nerve tissue, the mouths of the pores being
occupied by sense organs connected with these nerves. The tegmentum of
the six intermediate valves is generally divided into three triangular
areas by two more or less prominent ribs, which diverge from the
neighbourhood of the median _beak_ or _umbo_. The space enclosed
between these ribs is known as the _median area_ or _jugum_, the other
two spaces as the _lateral areas_ or _pleura_. The ribs terminate with
the edge of the tegmentum, and are not found on the articulamentum.
In certain genera these areas are either non-existent, or are not
distinctly marked. The sculpture of the lateral areas (which is, as
a rule, much stronger than that of the median area) will generally
be found to resemble that of the anterior valve, which has no proper
median area. In the posterior valve the median area is very small,
while the sculpture of the rest of the valve corresponds to that of the
lateral areas generally (see Fig. 261).
[Illustration: FIG. 263.--First, fourth, and eighth valves of a
_Chiton_, showing _l.i_, laminae of insertion; _n_, _n_, notches;
_s.l_, _s.l_, sutural laminae. × 2.]
The articulamentum of the intermediate valves is divided into two equal
parts in the middle of the anterior edge, opposite to the beak, by a
_sinus_. Each of the portions thus formed is again divided by a _notch_
or suture into two unequal parts, the anterior of which is known as
the _sutural lamina_, and is more or less concealed by the valve in
front of it, while the lateral part, or _lamina of insertion_, is
entirely concealed by the girdle. The articulamenta of the anterior and
posterior valves are either simple or pierced by a series of notches
(Fig. 263).
The girdle of the _Chitonidae_ varies considerably in character.
Sometimes its upper surface is simply corneous or cartilaginoid, with
no other sculpture than fine striae, at others it is densely beset with
spines or bristles, or tufted at intervals with bunches of deciduous
hairs; again it is marbled like shagreen or mossy down, or covered with
serpent-like scales. The width of the girdle varies greatly, being
sometimes very narrow, sometimes entirely covering all the valves
(_Cryptochiton_). As a rule, its outer edge is continuous, but in
_Schizochiton_ it is sharply notched over the anus.
A description has already been given of the dorsal eyes in Chiton (p.
187), the nervous system (p. 202), the branchiae (p. 154), the radula
(p. 228), and the generative system (p. 126).
[Illustration: FIG. 264.--Girdles of various Chitonidae. =A=,
_Radsia sulcata_ Wood, × 2; =B=, _Maugeria granulata_ Gmel., ×
3; =C=, _Enoplochiton niger_ Barnes, × 3; =D=, _Acanthochiton
fascicularis_ L., × 4; =E=, _Tonicia fastigiata_ Sowb., × 4.]
The recent Chitons are thus classified by Dr. W. H. Dall:--
SECTION I. CHITONES REGULARES.--_Anterior and posterior valves
of similar character._
A. _Leptoidea._--Insertion plates obsolete, or, if present,
unslit; _Leptochiton_, _Hanleyia_, _Hemiarthrum_, _Microplax_.
B. _Ischnoidea._--Insertion plates sharp, smooth, fissured; with
eaves; _Trachydermon_, _Callochiton_, _Tonicella_, _Schizoplax_,
_Leptoplax_, _Chaetopleura_, _Spongiochiton_, _Ischnochiton_,
_Callistochiton_.
C. _Lophyroidea._--Insertion plates broad, pectinated,
projecting backward; _Chiton_, _Tonicia_, _Eudoxochiton_,
_Craspedochiton_.
D. _Acanthoidea._--Insertion plates thrown forward;
_Sclerochiton_, _Acanthopleura_, _Dinoplax_, _Middendorffia_,
_Nuttallina_, _Arthuria_, _Phacellopleura_.
SECTION II. CHITONES IRREGULARES.--_Posterior valve abnormal, or
with a sinus behind._
E. _Schizoidea._--Posterior valve fissured; _Lorica_,
_Schizochiton_.
F. _Placiphoroidea._--Posterior valve unslit, internally
ridged, umbo nearly terminal; _Enoplochiton_, _Ornithochiton_,
_Plaxiphora_.
G. _Mopaloidea._--Posterior valve with posterior sinus and one
slit on each side; _Mopalia_, _Katherina_, _Acanthochiton_,
_Notoplax_.
H. _Cryptoidea._--With double sutural laminae; _Cryptoconchus_,
_Amicula_, _Cryptochiton_.
I. _Chitonelloidea._--Posterior valve funnel shaped; laminae
thrown forward; _Chitonellus_, _Choneplax_.
[Illustration: FIG. 265.--_Chitonellus fasciatus_ Quoy; _ant_,
anterior end.]
=Sub-order 2.= =Aplacophora.=--Animal vermiform, foot absent,
or a mere groove, cuticle more or less covered with spicules.
According to Marion, one of the principal authorities on the group, the
Aplacophora are perhaps Amphineura whose development has been arrested
at an early stage, their worm-like exterior being due to adaptation
to surroundings. They have hitherto been found chiefly in the N.
Atlantic and Mediterranean, generally at considerable depths, and
often associated with certain polyps in a way which suggests a kind of
commensalism.
FAM. 1. _Neomeniidae._--Foot a narrow groove, intestinal tube without
differentiated liver, kidneys with common exterior orifice, sexes
united, ctenidia present or absent. Genera: _Neomenia_ (Fig. 266),
_Paramenia_, _Proneomenia_, _Ismenia_, _Lepidomenia_, _Dondersia_.
[Illustration: FIG. 266.--_Neomenia carinata_ Tullb.: _a_, anus;
_gr_, ventral groove; _m_, mouth.]
[Illustration: FIG. 267.--_Chaetoderma nitidulum_ Lov.: _a_,
anus; _m_, mouth. × 3.]
FAM. 2. _Chaetodermatidae._--Body cylindrical, no ventral groove, liver
a single sac, kidneys with separate orifices into the branchial cloaca,
two bipectinate ctenidia. Single genus, _Chaetoderma_ (Fig. 267).
=Order II. Prosobranchiata=
Visceral loop twisted into a figure of 8 (streptoneurous), right half
supra-intestinal, left half infra-intestinal; heart usually in front
of the branchia (ctenidium), which is generally single; head with a
single pair of tentacles; animal dioecious, usually marine, more or
less contained within a shell, operculum generally present. Cambrian to
present time.
=Sub-order 1.= =Diotocardia.=--Heart with two auricles (except in the
_Docoglossa_ and _Helicinidae_), branchiae bipectinate, front end
free; two kidneys, the genital gland opening into the right (except in
Neritidae); nervous system not concentrated; no proboscis or siphon,
penis usually absent.
(_a_) DOCOGLOSSA (p. 227).--Heart with a single auricle, ventricle not
traversed by the rectum, visceral sac not spiral, shell widely conical,
non-spiral, no operculum; radula very long, with few hooked teeth in
each row.
FAM. 1. _Acmaeidae._--Left ctenidium alone occurring, free on a long
stalk. Cretaceous----. Principal genera: _Pectinodonta_, front part
of head much produced, radula 0 (1. 0. 1.) 0; _Acmaea_ (= _Tectura_),
with sub-genera _Collisella_ and _Collisellina_, no accessory branchial
ring, shell closely resembling that of _Patella_, but generally with a
distinct internal border; _Scurria_, accessory branchial ring on the
mantle.
FAM. 2. _Lepetidae._--No ctenidia or accessory branchiae, animal
generally blind. Pliocene----. Principal genera: _Lepeta_;
_Propilidium_, apex with internal septum; _Lepetella_.
FAM. 3. _Patellidae._--No ctenidia, the osphradial patch at the base
of each alone surviving, a circlet of secondary branchiae between the
mantle and sides of the foot. Ordovician----. (i.) _Patellinae._--Three
lateral teeth on each side, two of them anterior. Principal genera:
_Patella_, branchial circlet complete; chief sections _Patella_ proper,
_Scutellastra_, _Ancistromesus_ (_A. mexicana_ Brod., measures 8–14 in.
long); _Helcion_, branchial circlet interrupted in front; _Tryblidium_
(Ordovician).--(ii.) _Nacellinae._--Two developed laterals on each
side, one anterior. Genera: _Nacella_, branchial circlet complete;
_Helcioniscus_, branchial circlet interrupted in front.
(_b_) RHIPIDOGLOSSA (p. 225).--Ventricle of the heart traversed by the
rectum (except in Helicinidae), one or two ctenidia; jaw in two pieces,
radula long, marginals multiplied, rows curved.
Of all the Gasteropoda, this section of the Diotocardia approach
nearest to the Pelecypoda, particularly in the least specialised
forms. The auricle, the branchiae, and the kidneys are in many cases
paired, and more or less symmetrical. The ventricle is generally
traversed by the rectum, there is a long labial commissure between the
cerebral ganglia, special copulative organs are usually absent, while
the shell is often nacreous, like those of Pelecypoda of a primitive
type.
SECTION I. ZYGOBRANCHIATA.--Two ctenidia, shell with apical or marginal
slit or holes, corresponding to an anal tube in the mantle (p. 265).
FAM. 1. _Fissurellidae._--Two symmetrical ctenidia and kidneys,
visceral mass conical, shell conical, elevated or depressed, with
a single anterior or apical slit or impression; no operculum.
Jurassic----. (i.) _Fissurellinae_. Shell wholly external, apex
entirely removed by perforation, apical callus not truncated
posteriorly; central tooth narrow. Genera: _Fissurella_ (Figs. 171, p.
261; 178, p. 265), _Fissuridea_, _Clypidella_. (ii.) _Fissurellidinae_.
Shell partly internal, otherwise as in (i.); central tooth broad,
mantle more or less reflected over the shell, apical hole very wide.
Genera: _Fissurellidaea_, _Pupillaea_, _Lucapina_, _Megatebennus_,
_Macroschisma_, _Lucapinella_. (iii.) _Emarginulinae_. Shell usually
wholly external, apex usually not removed by perforation, sometimes
with internal septum, anal tube in a narrow slit or sinus. Genera:
_Glyphis_, externals of _Fissurella_, but holecallus truncated behind;
_Puncturella_ (sub-genera _Cranopsis_ and _Fissurisepta_), slit just
anterior to the apex, a small internal septum; _Zeidora_, large
internal septum as in _Crepidula_: _Emarginula_, shell elevated,
slit very narrow, on the anterior margin (in subg. _Rimula_, it is
between the apex and the margin), radula bilaterally asymmetrical;
_Subemarginula_, margin indented by a shallow groove; _Scutus_ (=
_Parmophorus_) shell oblong, depressed, nicked in front, largely
covered by the mantle.
[Illustration: FIG. 268.--_Scutus australis_ Lam., Australia:
_m_, _m_, mantle; _sh_, shell, × ⅔.]
FAM. 2. _Haliotidae_.--Right ctenidium the smaller, epipodial line
broad, profusely lobed; shell rather flattened, spire short, last
whorl very large, with a row of perforations on the left side, which
become successively obliterated; through these holes, the posterior of
which is anal, pass tentacular appendages of the mantle; no operculum.
Cretaceous----. Single genus, _Haliotis_; principal sub-genera
_Padollus_, _Teinotis_.
FAM. 3. _Pleurotomariidae_.--Central tooth single, narrow, about 26
laterals, 60 to 70 uncini. Shell generally variously trochiform,
nacreous, operculate, with a rather broad marginal sinus in the last
whorl; as this sinus closes up it forms an “anal fasciole” or “sinus
band.” Cambrian----. Principal genera: _Scissurella_, epipodial line
with several long ciliated appendages at each side, shell very small,
slit open, sinus band extending nearly to apex; _Schismope_, anal
slit closed in the adult into an oblong perforation; _Murchisonia_
(Palaeozoic only), shell long, turreted, whorls angulate or keeled
with a sinus band; _Odontomaria_ (Palaeozoic only), shell tubular,
curved; _Polytremaria_ (Carboniferous), shell turbinate, slit a series
of small holes connected by a passage; _Trochotoma_, shell trochiform,
perforation consisting of two narrow holes united by a slit;
_Pleurotomaria_, branchiae almost symmetrical, radula as above, shell
variously spiral.
In _Pleurotomaria_ we have the case of a genus long supposed to be
extinct. More than 1100 fossil species have been described, and within
the last 38 years about 20 specimens, belonging to 5 species, have been
discovered in a living state.
[Illustration: FIG. 269.--_Pleurotomaria adansoniana_ Cr. and F.,
Tobago. × ½.]
FAM. 4. _Bellerophontidae_.--Shell nautiloid, spire generally
concealed, aperture large, sinus or perforations central (Fig. 179,
p. 266). Ordovician--Trias. Genera: _Bellerophon_, _Trematonotus_,
_Cyrtolites_.
SECTION II. AZYGOBRANCHIATA.--One ctenidium (the left) present.
FAM. 1. _Cocculinidae._--A single cervical ctenidium, foot broad,
no eyes, shell patelliform, with caducous spire. Single genus,
_Cocculina_. Deep water.
FAM. 2. _Stomatellidae._--A single (left) ctenidium, front third
free, shell nacreous, spiral or patelliform, depressed, last whorl
large. Jurassic----. Genera: _Stomatella_ (subg. _Synaptocochlea_,
_Niphonia_), shell depressed, spirally ribbed, spire short, operculum
present; _Phaneta_, fluviatile only, shell trochiform, imperforate,
last whorl keeled, sinuate in front; _Stomatia_, spire short, surface
tubercled or keeled, no operculum; _Gena_, shell haliotis-shaped,
surface smooth, aperture very large; _Broderipia_, shell patelliform,
spiral apex often lost.
FAM. 3. _Cyclostrematidae._--Tentacles ciliated, thread-like, snout
bilobed, foot truncated in front, angles produced into a filament,
shell depressed, umbilicated, not nacreous. Eocene----. Principal
genera: _Cyclostrema_, _Teinostoma_, _Vitrinella_.
FAM. 4. _Liotiidae._--Epipodial line with a lobe behind each
eye-peduncle, shell solid, trochiform, longitudinally ribbed or
trellised, aperture round, operculum multispiral, hispid, corneous,
with a calcareous layer. Silurian----. Principal genera: _Liotia_,
_Craspedostoma_ (Silurian), _Crossostoma_ (Jurassic).
[Illustration: FIG. 270.--_Monodonta canalifera_ Lam., New
Ireland. (After Quoy and Gaimard.)]
FAM. 5. _Trochidae._--Snout short, broad, frontal lobes often present,
epipodial line furnished with cirrhi; shell nacreous, variously spiral,
operculum corneous, multispiral, nucleus central (Fig. 182, p. 268).
Silurian----. (i.) _Trochinae._--Frontal lobes present, lateral teeth
(= side centrals) 5 only, no jaws, peristome incomplete. Principal
genera: _Trochus_ (subg. _Cardinalia_, _Tectus_, _Infundibulum_,
_Clanculus_), _Monodonta_ (subg. _Diloma_), _Cantharidus_ (subg.
_Bankivia_, _Thalotia_), _Gaza_ (subg. _Microgaza_), _Callogaza_,
_Bembix_, _Chlorostoma_. (ii.) _Gibbulinae._--Frontal lobes and
jaws present, laterals often more than 5, peristome incomplete.
Principal genera: _Gibbula_ (subg. _Monilia_, _Aphanotrochus_,
_Enida_), _Minolia_, _Circulus_, _Trochiscus_, _Livona_, _Photinula_,
_Margarita_, _Solariella_, _Calliostoma_, _Turcica_, _Basilissa_,
_Euchelus_ (subg. _Olivia_, _Perrinia_). (iii.) _Delphinulinae._--No
frontal lobes, jaws present; shell solid, surface spirally lirate,
scaly, spinose, umbilicate, peristome continuous. Single genus,
_Delphinula_. (iv.) _Umboniinae._--Eyes pedunculate, left tentacle
attached to a frontal appendage, mantle reflected over edge of
aperture, lateral teeth 6 on each side; shell polished, peristome
incomplete, umbilicus generally closed by a callosity. Principal
genera: _Umbonium_, _Ethalia_, _Isanda_, _Camitia_, _Umbonella_,
_Chrysostoma_.
[Illustration: FIG. 271.--_Phasianella australis_ Gmel.,
Australia.]
FAM. 6. _Turbinidae._--Epipodial line with slender cirrhi, snout
broad, short, eyes pedunculate at outer base of tentacles, a frontal
veil between tentacles; shell turbinate, solid, aperture continuous,
operculum solid, calcareous, usually paucispiral, convex exteriorly
(Fig. 182, p. 268). Silurian----. (i.) _Phasianellinae._--Shell
bulimoid, polished, not nacreous, coloured in patterns, aperture oval.
Single genus, _Phasianella_ (Fig. 271). (ii.) _Turbininae._--Shell
very solid, nacreous within, aperture circular or long oval. Principal
genera, _Turbo_, whorls rounded above and below, spines, if present,
becoming more prominent with age, operculum smooth or granulose,
nucleus sub-central; subg. _Callopoma_, _Ninella_, _Marmorostoma_,
_Sarmaticus_, _Prisogaster_; _Astralium_, whorls flattened above and
below, spines, if present, becoming less prominent with age, operculum
oblong, often excavated at centre, last whorl large, nucleus marginal
or sub-marginal; subg. _Lithopoma_, _Imperator_, _Guildfordia_,
_Bolma_, _Cyclocantha_, _Uvanilla_, _Cookia_, _Pomaulax_,
_Pachypoma_. (iii.) _Cyclonematinae._--Shell nacreous, umbilicate,
operculum conical outside, whorls scalariform. Principal genera:
_Cyclonema_, _Horiostoma_ (?), _Amberleya_ (Silurian to Lias). (iv.)
_Leptothyrinae._--Shell small, solid, depressed, operculum nearly flat,
nucleus sub-central. Genera: _Leptothyra_, Collonia (?).
FAM. 7. _Neritopsidae._--Tentacles wide apart, long, eyes on short
peduncles at the outer base; shell solid, neritiform or naticoid,
aperture semi-lunar or oval; operculum (Fig. 183, p. 269) thick,
calcareous, non-spiral, exterior face smooth, interior face divided
into two unequal parts, with a broad median appendage. Devonian----.
Principal genera: _Neritopsis_ (one recent species), _Naticopsis_
(Devonian to Miocene).
FAM. 8. _Macluritidae._--Shell discoidal, whorls few, longitudinally
grooved behind, right side convex, deeply umbilicated, left side flat;
operculum very thick, nucleus excentrical, internal face with two
apophyses, one very large. The general appearance is more that of an
inequivalve bivalve, such as _Requienia_, than of a spiral gasteropod.
Palaeozoic----. Single genus, _Maclurea_.
FAM. 9. _Neritidae._--Snout short, tentacles long, eyes pedunculate
at their outer base, branchia triangular, free at the front end,
epipodium without cirrhi, penis near the right tentacle; shell
solid, imperforate, turbinate to almost patelliform, spire short,
internal partitions absorbed (p. 168), columellar region broad, edge
simple or dentate, operculum calcareous, spiral or non-spiral, with
prominent apophyses on the interior face, one of which locks behind
the columellar lip. Jurassic----. Principal genera: _Nerita_ (Fig. 13,
p. 17); _Neritina_ (chiefly brackish water and fluviatile), sub-genus
_Clithon_, usually coronated with spines; _Velates_ (Tertiary),
_Neritoma_ (Jurassic), _Deianira_ (Cretaceous), _Septaria_ (=
_Navicella_), shell more or less narrowly patelliform, with terminal
apex, aperture very large, with a broad columellar septum, operculum
too small for the aperture, more or less covered by the integument of
the foot; fluviatile only; _Pileolus_ (Jurassic to Cretaceous).
FAM. 10. _Hydrocenidae._--Branchia replaced by a pulmonary chamber,
eyes at the outer base of the tentacles, marginals of the radula very
oblique, centrals often wanting; shell small, conical, whorls convex,
operculum calcareous, with a prominent apophysis. Recent. Principal
genera: _Hydrocena_, _Georissa_.
FAM. 11. _Helicinidae._--Branchia replaced by a pulmonary chamber,
heart with one auricle; shell globular, with a short spire, internal
partitions absorbed; operculum without apophysis. Carboniferous----.
Principal genera: _Helicina_ (Fig. 18B, p. 21; subg. _Alcadia_,
_Schasicheila_, _Heudeia_, _Calybium_), _Eutrochatella_ (subg.
_Lucidella_), _Stoastoma_, _Bourcieria_, _Dawsonella_ (Carboniferous).
FAM. 12. _Proserpinidae._--Branchia replaced by a pulmonary chamber,
mantle partly reflected over the shell, eyes sessile; shell depressed,
discoidal, columella folded or truncated at the base, whorls with one
or more internal plicae, internal partitions absorbed, no operculum.
Eocene----. Single genus; _Proserpina_, subg. _Proserpinella_, _Cyane_,
_Dimorphoptychia_ (Eocene), and _Ceres_ (Fig. 18C, p. 21).
=Sub-order II.= =Monotocardia.=--Heart with one auricle, one ctenidium
(the left), monopectinate, fused with the mantle (except in _Valvata_),
one kidney, not receiving the genital products, nervous system somewhat
concentrated, proboscis and penis usually present.
(_a_) PTENOGLOSSA.--Radula with formula ∞. ᴑ. ∞, teeth similar
throughout, outermost largest (p. 224).
FAM. 1. _Ianthinidae._--Snout prominent, blunt, no eyes, shell
helicoid, fragile, bluish, no operculum; eggs carried on a raft of
vesicles attached to the foot (Fig. 42, p. 126). Pelagic only. Pliocene
----. Genera: _Ianthina_, _Recluzia_.
FAM. 2. _Scalariidae._--Shell long, turriculate, whorls often partly
uncoiled, with longitudinal ribs and prominent lamellae, aperture
circular, operculum spiral, corneous, animal carnivorous. Ordovician
----. Principal genera: _Scalaria_, _Eglisia_, _Elasmoneura_
(Silurian), _Holopella_ (Silurian to Trias), _Aclis_.
(_b_) TAENIOGLOSSA.--Radula with normal formula 2.1.1.1.2, marginals
sometimes multiplied (p. 223).
SECTION I. PLATYPODA.--Foot more or less flattened ventrally.
FAM. 1. _Naticidae._--Foot very large, produced before and behind,
propodium reflected upon the head, eyes absent or buried in the
integument, central and lateral tooth of the radula tricuspid,
middle cusp strong; shell globular or auriform, outer lip simple,
operculum corneous or calcareous, nucleus excentrical. Carboniferous
----. Principal genera: _Natica_, with many sub-genera; _Ampullina_
(Tertiary); _Amaura_; _Deshayesia_ (Tertiary); _Sigaretus_ (Fig. 91, p.
186), shell auriform, last whorl very large, operculum much too small
for the aperture.
FAM. 2. _Lamellariidae_.--Mantle reflected over more or less of the
shell, shell delicate, no operculum. Eocene----. Principal genera:
_Lamellaria_, shell completely internal, transparent, auriform; some
species deposit their eggs on compound Ascidians (p. 74); _Velutina_,
shell almost entirely external, paucispiral, with a thick periostracum;
_Marsenina_, shell auriform, partly internal; _Onchidiopsis_, shell a
membranous plate, internal.
FAM. 3. _Trichotropidae._--Branchial siphon short, eyes on the outer
side of the tentacles; radula closely allied to that of _Velutina_;
shell conical, last whorl rather large, periostracum thick and hairy,
operculum blunt claw-shaped, nucleus terminal. Cretaceous----. Genera:
_Trichotropis_, _Torellia_.
FAM. 4. _Naricidae._--Tentacles broad in the middle, with sessile eyes
at the exterior base, propodium narrow, quadrangular, a large epipodial
veil on each side of the foot; shell naticoid, cancellated, with
velvety periostracum. Jurassic----. Single genus: _Narica_.
FAM. 5. _Xenophoridae._--Foot divided by a groove, anterior portion
the larger; central tooth heart-shaped, with blunt cusps, lateral
large, roughly triangular, marginals long, falciform; shell trochiform,
somewhat flattened, attaching various fragments externally.
Devonian----. Single genus, _Xenophora_ (Figs. 25, 26, p. 64).
FAM. 6. _Capulidae._--Ctenidium deeply and finely pectinate, visceral
sac scarcely spiral, penis long, behind the right tentacle; shell
roughly patelliform, with scarcely any spire, interior polished,
usually with a septum or internal plate of variable form, no operculum.
Devonian----. Principal genera (Fig. 155, p. 248); _Capulus_, shell
cap-shaped, no internal plate; _Platyceras_ (Palaeozoic, see p. 76),
_Diaphorostoma_ (Palaeozoic), _Addisonia_ (?); _Crucibulum_, internal
appendage funnel-shaped; _Crepidula_ (including _Crepipatella_ and
_Ergaea_), shell slipper-shaped, with a large septum; _Calyptraea_
(including _Galerus_ and _Trochita_), internal lamina semi-spiral.
FAM. 7. _Hipponycidae._--Foot aborted, animal sedentary,
adductor-muscle shaped like a horse’s hoof, fastened on the ventral
side to the region of attachment, or to a thin calcareous plate which
closes the aperture like a valve; ventral side of the body surrounded
by a mantle with papillose border, which corresponds morphologically
to the epipodia, head emerging between the dorsal and ventral mantles.
Shell thick, bluntly conical, surface rugose. Eocene----. Genera:
_Hipponyx_; _Mitrularia_, a narrow half funnel-shaped appendage within
the shell.
[Illustration: FIG. 272.--Two specimens of _Crepidula_ (marked
_a_ and _b_) on an old shell of _Murex radix_ Gmel.]
FAM. 8. _Solariidae._--Foot large, eyes sessile, near the outer
base of the tentacles, radula abnormal (p. 224); shell more or less
depressed, lip simple, umbilicus wide, margins often crenulated,
operculum variable. The proper position of the family is quite
uncertain. Ordovician----. (i.) _Solariinae_. Genera: _Solarium_,
shell depressed, highly finished, angular at periphery, operculum
corneous, central tooth absent, laterals and marginals numerous, long,
and narrow; _Platyschisma_ (Silurian). (ii.) _Toriniinae._ Genera:
_Torinia_, whorls usually rounded, operculum (Fig. 183) conically
elevated, spiral externally, central tooth present, marginals few, edge
pectinated; _Omalaxis_. (iii.) _Euomphalinae_, shell planorbiform,
whorls rounded. Genera: _Euomphalus_, _Ophileta_, _Schizostoma_,
_Eccyliomphalus_ (all Palaeozoic).
FAM. 9. _Homalogyridae._--Tentacles absent, eyes sessile, central tooth
unicuspid on a quadrangular base, laterals and marginals replaced by
an oblong plate; shell very small, planorbiform. Recent. Single genus:
_Homalogyra_, whose true position is uncertain.
[Illustration: FIG. 273.--_Solarium perspectivum_ Lam., Eastern
Seas.]
FAM. 10. _Littorinidae._--Proboscis short, broad, tentacles long, eyes
at their outer bases, penis behind the right tentacle; reproduction
oviparous or ovoviviparous, radula very long; shell turbinate,
solid, columella thickened, lip simple, operculum corneous, nucleus
excentrical. Jurassic----. Principal genera: _Littorina_ (radula, Fig.
16, p. 20), _Cremnoconchus_ (p. 16), _Fossarina_; _Tectarius_, shell
tubercled or spinose; _Risella_, base slightly concave; _Lacuna_, shell
thin, grooved behind the columellar lip.
FAM. 11. _Fossaridae._--Shell turbinate, solid, small, white, spirally
ribbed, outer lip simple. Miocene----. Principal genus, _Fossarus_.
FAM. 12. _Cyclophoridae._--Ctenidium replaced by a pulmonary
sac, tentacles long, thread-like (radula, Fig. 17, p. 21); shell
variously spiral, peristome round, often reflected, operculum
circular. Terrestrial only. Cretaceous----. (i.) _Pomatiasinae_,
shell high, conical, longitudinally striated, operculum consisting
of two laminae united together. Single genus, _Pomatias_. (ii.)
_Diplommatininae_, shell more or less pupiform, peristome thickened
or reflected, often double. Genera: _Diplommatina_ (subg., _Nicida_,
_Palaina_, _Paxillus_, _Arinia_), shell dextral or sinistral, small,
columella often denticulated; _Opisthostoma_ (Fig. 208, p. 309),
last whorl disconnected, often reflected back upon the spire. (iii.)
_Pupininae_, shell more or less lustrous, bluntly conical, lip with
a channel above or below. Genera: _Pupina_ (subg., _Registoma_,
_Callia_, _Streptaulus_, _Pupinella_, _Anaulus_), _Hybocystis_ (Fig.
205, p. 305), _Cataulus_, _Coptochilus_, _Megalomastoma_. (iv.)
_Cyclophorinae_, shell turbinate or depressed, operculum corneous
or calcareous. Genera: _Alycaeus_, _Craspedopoma_, _Leptopoma_,
_Lagochilus_, _Cyclophorus_ (Fig. 206, p. 306); including _Diadema_,
_Aulopoma_, _Ditropis_, and others), _Aperostoma_ (including
_Cyrtotoma_ and others), _Cyathopoma_, _Pterocyclus_ (subg.,
_Myxostoma_, _Spiraculum_, _Opisthoporus_, and _Rhiostoma_ (Fig. 180,
p. 266), _Cyclotus_, _Cyclosurus_, and _Strophostoma_.
FAM. 13. _Cyclostomatidae._--Ctenidium replaced by a pulmonary sac,
tentacles obtuse, foot with a deep longitudinal median groove; central
tooth, lateral, and first marginal more or less bluntly cusped, second
marginal large, edge pectinate; shell variously spiral, spire usually
elevated, aperture not quite circular; operculum generally with an
external calcareous and an internal cartilaginoid lamina, rarely
corneous. Terrestrial only. Cretaceous----. Genera: _Cyclostoma_
(subg., _Leonia_, _Tropidophora_, _Rochebrunia_, _Georgia_, _Otopoma_,
_Lithidion_, _Revoilia_), _Cyclotopsis_, _Choanopoma_ (subg., _Licina_,
_Jamaicia_, _Ctenopoma_, _Diplopoma_, _Adamsiella_), _Cistula_
(subg., _Chondropoma_, _Tudora_), _Omphalotropis_ (subg., _Realia_,
_Cyclomorpha_), _Hainesia_, _Acroptychia_.
[Illustration: FIG. 274.--_Cyclostoma campanulatum_ Pfr.,
Madagascar.]