CHELONOBIA. _Leach._ Journal de Physique, tom. 85, (1817).
CORONULA. _Lamarck._ Animaux sans Vertèbres, 1818.
---- _Ranzani._ Memoire di Storia Naturale, 1820.
---- _De Blainville._ Dict. des Sciences Naturelles.
ASTROLEPAS. _J. E. Gray._ (Klein) Annals of Philosophy, (new series),
vol. 10, (1825).
_Compartments extremely thick, six; but one of them, the rostrum,
internally is composed of three rudimentary compartments, united
together: basis membranous: scuta narrow, united to the terga by a
horny articular ridge._
_Distribution_, throughout the tropical, and warmer temperate seas of
the whole world; attached to turtles, crustacea, or smooth gasteropod
molluscs.
This is a distinct and well-defined genus. Several authors have
confounded it with Coronula, but this has been owing to an entire
misapprehension of the structure of the shell in the two genera. In
Coronula, the parietes are very thin, and are so deeply folded as to
appear like rays or septa connecting the outside of the shell (the
expanded ends of the folds) and the internal surface of the shell, but
the open spaces between the folds are occupied by the epidermis of the
Whale, and are external to the cirripede. In Chelonobia, the parietes
are remarkably thick; hence the plates or septa, connecting the outer
and inner lamina, are of unusual length; and the spaces between them,
though of course internal with regard to the cirripede and occupied by
the ovaria, have been compared to the spaces external to and between
the folded walls of Coronula. There is but little special affinity
between these genera; and I regret that they have come to be placed one
after the other in this work: but the elongated opercular valves,--the
thick and double opercular membrane,--the weak depressor muscles,--and
the peculiar manner in which the scutum is articulated by the aid of
a horny projection to the tergum, may indicate some real but slight
affinity to Coronula; the many points of difference, however, in the
structure of the shell and of the opercular valves, and especially in
the cementing apparatus of the basal membrane, and in the branchiæ,
all prove that the genera are very distinct. The singular structure of
the rostrum, which, in fact, consists of three compartments externally
blended together, and which three correspond in all essential respects
to the rostrum and two rostro-lateral compartments in the Chthamalinæ,
offers a very striking point of identity with that sub-family; but
neither in the mouth, cirri, or other part, can I detect any other
evidence of this relationship. Having so far discussed the affinities
of the genus, I may add, that the three species, though decidedly
distinct, are closely and nearly equally related to each other.
_General Appearance._--The shell is generally depressed, and broadly
oval or almost circular; in _C. testudinaria_ and _caretta_, it
has a massive appearance: the surface is generally smooth, or,
when disintegrated, finely striated: the colour is white. The six
compartments do not differ much in size: the rostrum is rather larger
than the carina, and the lateral compartments, than the carino-lateral
compartments. It is remarkable that in _C. caretta_ (Pl. 14, fig.
2), even in specimens which have not grown crowded together, the
compartments are almost invariably placed rather unsymmetrically,
the rostrum and carina not exactly facing each other.[121] The shell,
though so thick and massive, yields easily along the lines of suture.
The radii are moderately wide, or narrow, or not at all developed,
being represented by mere sutures: in this latter case, in _C.
caretta_, the orifice of the shell is enlarged, in the same manner as
we have seen in some species of Balanus and Tetraclita, by the gradual
wearing away of the upper part of the shell. In _C. testudinaria_,
the radii have a singular notched structure (fig. 1 _a_), and the
whole shell a star-like appearance. The orifice is not filled up by
the elongated opercular valves,--a considerable extent of opercular
membrane being visible on the two sides. The largest specimen which
I have seen, namely, of _C. testudinaria_, was nearly two and a half
inches in its longer diameter.
[121] In Mr. Stutchbury's collection there is a specimen of _C.
testudinaria_ in which there are only five compartments, one of the
lateral compartments having been aborted; of this I have seen no
other instance in any genus.
_Structure of the Parietes._--The parietes are of unequalled thickness,
especially in the first two species of the genus. From the outer lamina
(see Pl. 14, fig. 4, and the section in Pl. 15, fig. 1), numerous
vertical plates extend inwards, alternately to a less or greater
distance, some of them reaching to the inner lamina: these answer to
the longitudinal parietal septa in other genera, and the elongated
cavities between them (which occur in _C. testudinaria_ and _patula_)
answer to the parietal tubes or pores. The radiating plates or septa
have their sides finely channelled, and their basal edges generally
slightly sinuous and always finely toothed. The interspaces between
the plates in the uppermost part of the shell are filled up solidly,
and, in _C. caretta_, even down to near the basis: in this latter
species, the plates are irregular and much broken up, so as in parts
to consist of little, separate, flattened points. In _C. patula_, the
inner lamina of the parietes (_b_, in fig. 4. Pl. 14) can be best
made out to be distinct from the sheath (_e c e_ in fig. 4, and _c′_
in the section of _C. testudinaria_, fig. 1, Pl. 15). The sheath in
this genus descends in a very remarkable manner to the basal membrane,
and has its basal edge toothed like the basal edges of the radiating
septa. The inner lamina itself does not descend to the basal membrane.
In _C. testudinaria_, the inner lamina is of great thickness; but in
the section, (fig. 1) owing to its having been taken high up, the
inner lamina, (_b_), is not distinct from the shelly matter deposited
between the septa. In _C. caretta_, the line of separation between the
inner and outer laminæ can in no part be distinguished, owing to the
interspaces between the septa having been solidly filled up, close down
to the basis.
_Sheath._--The layer of shell surrounding the internal cavity (_e c
e_, fig. 4, Pl. 14), and extending down to the basal membrane, I have
called the sheath, owing to its being distinctly continuous with the
innermost layer in the upper part of the shell, to which the opercular
membrane is attached: this can be best seen by examining the alæ in
the separated compartments of _C. patula_. The sheath is not only
remarkable from thus descending to the basal membrane, but in _C.
testudinaria_ and _patula_ from its lower edge being perforated by
arched channels (under _c_, in fig. 4), allowing thick ribbons of
corium to reach the interspaces between the radiating septa. There
is one central arch or channel in the middle of the lower part of
the sheath of each compartment, and one on each line of suture, the
sheath being a little hollowed out on both sides of the sutures. As the
rostrum, as far as its internal structure is concerned, consists of
three compartments, we have altogether in the shell eight compartments
and eight sutures, and consequently altogether sixteen arches through
the lower part of the sheath, allowing sixteen thick ribbons of corium
to penetrate the parietes, and thus likewise reach the radii. There is,
however, sometimes a little variation in the number of these arched
channels. The upper part of the sheath is transversely marked by
zones of growth, to the lower one of which the opercular membrane is
attached. The line of attachment is not low down the sheath.
_Radii and Alæ._--The radii, when the compartments are disarticulated,
present a remarkable structure, from appearing to consist of a distinct
inner and outer portion. The radius normally consists of an inner and
outer lamina, united by septa parallel to the basis; but here the inner
portion is formed by a central ridge (_a a_, fig. 5, Pl. 14), sending
off on both sides little septa, often sub-branched; it is of nearly
uniform width; and there is no distinct inner lamina. The outer portion
(_b_), which often equals or exceeds in thickness the inner portion,
is, in fact, the normal outer lamina, developed to an unparalleled
degree. In most Cirripedes the edge of the radius is received in a
slight furrow in the opposed compartment, the lid of which furrow is
narrow, and matches the outer lamina of the radius; here the lid of the
recipient furrow is very broad, and resembles the outer lamina of the
radius in all its characters. In order to allow of growth between the
_thick_ opposed edges of the outer lamina of the radius and the lid of
the recipient furrow, the two surfaces are finely dentated (look in
fig. 5, under the pits, marked _b_), almost like the crown of a molar
tooth; thus allowing films of corium to enter. The structure here
described is common, in a greater or less degree, to all three species,
but is best seen in _C. testudinaria_. In this species, moreover, (fig.
5, _b_), the outer lamina, instead of being smooth and of either equal
or gradually increasing thickness from top to bottom, is generally, but
not always, (fig. 1 _a_), deeply pitted or notched in transverse lines,
the outer lamina being thus rendered alternately thicker and thinner,
and so formed into transverse ridges and valleys. Hence the lines of
suture become toothed, the points of the teeth facing each other, and
not interlocking. In the transverse section, fig. 1, Pl. 15, of the
same species, taken high up across the shell, (_f_) is the pitted outer
lamina, and (_e_) the inner portion of the radius. Although the radii
are thus specially added to in thickness, they are not so thick as the
very thick walls, and hence the lines of suture form furrows more or
less deep. The _alæ_ are of moderate thickness, and have their sutural
edges crenated by fine transverse septa.
_Rostrum._--I have already alluded to the peculiar compounded structure
of this compartment, unlike anything we have as yet seen.[122] The
thin outer lamina is quite continuous, and shows no trace of the
triple nature of the compartment; as may be seen by comparing the
drawing (Pl. 14, fig. 1 _a_) of the shell of _C. testudinaria_,
with the transverse section (Pl. 15, fig. 1) of the same species:
in this latter figure, _a_ is the outer lamina, and B A B the three
compartments of the rostrum. But when the outer lamina is worn away,
as is always the case with the upper part of the walls in _C. caretta_
(Pl. 14, fig. 2), the two fissures separating the three compartments
of the compounded rostrum, are plainly exhibited on the outside of
the upper part of the shell. On the internal surface, the sutures
separating the three compartments are always open, except in the upper
part of the sheath, above the attachment of the opercular membrane,
where they are partially obliterated by a thin continuous layer of
shell. That these three portions of the rostrum are in their essential
nature compartments, is well shown in _C. patula_ and _testudinaria_,
by the sheath or inner lamina having loopholes or channels (such as
before described) in the middle of each, and on each line of suture.
From the number of these channels, seven altogether, (the two between
the compound rostrum and lateral compartments being counted,) the
sheath of the compound rostrum is reduced to mere flattened pillars
between the several channels. By slight violence, the rostrum breaks
into the three portions; and the sutures between them are found to be
marked on both sides by sinuous, slight, calcareous ridges, those on
opposite sides locking into each; these represent the septa on the
edges of the radii and alæ and their recipient furrows, in the ordinary
compartments. The outline of the middle compartment of the three (best
seen in section Pl. 15, fig. 1, A), much resembles that of the carina;
in fact, if we suppose the growth of the two alæ of the carina to have
been arrested, no essential difference can be pointed out: in this
rudimentary compartment, therefore, we have a rostrum, characterised as
in the sub-family of the Chthamalinæ. In the two little rostro-lateral
compartments, moreover, (B B), a slight swelling on the side opposite
to the large existing radius, shows that if the development of these
compartments had not been prevented, each, probably, would have
had, exactly as in the Chthamalinæ, a radius on both sides. In the
introduction to the Balanidæ, I have argued, from the structure here
described and from some other facts, that in the Balaninæ the rostrum
is composed of the three anterior compartments, which we see in the
Chthamalinæ, indissolubly united together; hence in Chelonobia the
middle one of the three partially-blended compartments is properly the
rostrum, and those on the sides the rostro-lateral compartments.
[122] My attention was first called to this peculiar structure of
the rostrum by Mr. Stutchbury.
_Basis._--The basal membrane extends under the thick walls to the
outside. I was not able to make out the whole cementing apparatus.
The main trunk is remarkable from its small diameter, (_f f_ in fig.
2, Pl. 28), and from the distance at which the cement-glands stand
apart. Each gland gives rise to a pair of cement-ducts, which tend to
run in parallel groups; these ducts repeatedly bifurcate, occasionally
inosculate, and decrease in diameter; they debouch and allow the cement
to escape at numerous points, placed at irregular distances, on the
edges of each new slip of the basal membrane.
_Opercular Valves._--These are elongated; they do not fill the orifice
of the shell; they are attached by a strong opercular membrane a little
way down the sheath. The opercular membrane is generally double, for
the last-formed membrane is not immediately moulted as soon as a new
one is formed, as generally happens in Balanus. Externally, the valves
are marked by rather rugged, broad zones of growth. The _Scuta_ are
elongated in the line of the orifice of the sack; the occludent margin
(Pl. 14, fig. 1 _b_) is much inflected, and generally sinuous; along
this inflected portion a distinct square-edged ridge runs, which widens
from the apex downwards. The depression for the adductor muscle is
very deep: there are no pits or crests for the other muscles. When the
scutum is thoroughly cleaned and all the membrane removed by caustic
potash, the tergal margin is marked by a slight articular ridge and
furrow. This articular ridge is very remarkable from supporting a
prominent, flattened crest (fig. 1 _b_), composed of hard, yellow,
horny membrane, which overlaps the inner surface of the tergum,
and exactly corresponds, in shape and purpose, with the calcareous
articular ridge, when best developed in other genera. Beneath the basal
and generally slightly sinuous exterior margin of the valve, that is,
the margin to which the opercular membrane is attached, a slight
ledge depends (fig. 1 _d_), which narrows off towards the rostral end
of the valve. I should have thought that this had been a depending
adductor ridge, as in several species of Pyrgoma, had there not been
a nearly similar ledge beneath the middle part of the basal margin of
the tergum. The _Tergum_ is mitre-formed, with the summit more or less
truncated, and with the carinal margin generally more sloping than the
scutal margin: near the carinal margin there is a slight furrow (fig. 1
_d_), sometimes difficult to be distinguished, with the lines of growth
curving down to it on each side, and consequently with a very slight,
but variable, corresponding projection on the basal margin. This furrow
and slight projection, there can be hardly any doubt, represent the
spur, though here placed close to the carinal instead of to the scutal
margin, as in other genera. The tergum has a small articular ridge,
against which the overlapping horny articular ridge of the scutum
abuts. There are no crests for the tergal depressor muscles. Altogether
the scuta and terga are very peculiar. A portion dissolved in acid
exhibits no tubuli. On the opercular membrane there are no hairs. The
rostral depressor muscles of the scuta are singularly feeble, each
consisting of only one or two, or sometimes three or four, very thin
ribbon-like fasciæ; the lateral depressores of the scutum are twice as
strong as the rostral depressores; and the tergal depressores a little
stronger than the lateral depressores. All these muscles are plainly
marked with transverse striæ.
_Mouth._--The labrum is not in the least bullate, which character, as
well as some others that follow, I specify on account of the apparent
affinity of Chelonobia to the Chthamalinæ, as indicated by its rostrum.
The crest of the labrum is notched, and on each side of the notch there
is a long row of teeth, which, however, are sometimes worn away. The
mandibles have five main teeth; all excepting the first being laterally
double. The maxillæ are not notched. The outer maxillæ are bilobed on
their inner sides.
_Cirri._--The four posterior pairs, in proportion to the size of the
animal, are much elongated, and are remarkable from the number of their
short segments. The rami of the first cirrus are a little unequal in
length. The second cirrus is moderately short, with its segments
rather broad and protuberant, and thickly clothed with spines. The
third cirrus is of unusual length, being but little shorter than the
fourth pair; its segments, however, are broad, and are thickly clothed
with spines, as are the two segments of its pedicel: hence there is no
real approach to that important character of the Chthamalinæ, namely,
the similarity of the third with the three posterior pairs of cirri.
The numerous segments of the fourth, fifth, and sixth pairs of cirri
each support only two pairs of main spines; between each of these pairs
there is a little tuft of fine intermediate spines; the upper of the
two tufts on each segment is the longest. In a specimen of _C. patula_,
in which there were fifteen segments in one ramus of the second cirrus,
there were fifty segments in either ramus of the sixth cirrus. At the
exterior bases of the pedicels of some of the anterior cirri, there are
large tufts of finely plumose, delicate hairs.
_Branchiæ._--These are of large size: they consist of a single fold,
much plicated and sub-plicated.
_Ovaria._--The ovarian tubes run into the parietes, and fill up the
interspaces between the radiating septa.
_Range, &c._--The three species seem to range together, over the
tropical and warmer temperate seas of the whole world. _C. patula_
and _testudinaria_ are found in the Mediterranean, and the former at
Charleston, in the United States; I have not heard of specimens from
any point further north. _C. testudinaria_ and _caretta_ live attached
to turtles; whilst _C. patula_ always adheres to crustacea, to large
and smooth gasteropod mollusca, and, I believe, sometimes to ships'
bottoms. I have not heard of the discovery of any fossil species.
_Attachment._--_Chelonobia patula_ leaves no impression on the crabs
and shells to which it is attached. I have seen only a few specimens
of _C. testudinaria_ attached, and the carapaces of the turtle were
not at all, or scarcely at all, indented by them. The case is very
different with _C. caretta_, in which the shell, even of young
specimens, is always, as far as I have seen, imbedded to some depth,
and occasionally to a very great depth in the tortoise-shell. From
the extreme hardness of the tortoise-shell, when dry, the imbedment
appears more wonderful even than it really is. The younger shells have
the appearance of having grown from within the carapace, and then of
having burst through it, almost like little volcanos. I have seen
only one very young shell (1/10th of an inch in external diameter)
attached, and here there was nothing to countenance an idea which at
one time occurred to me, namely, that the larva perhaps fixed itself in
some little crack or cavity in the carapace, and there underwent its
metamorphosis. I believe that the imbedment is effected simply by the
sharp, growing, basal edges of the walls of the shell indenting the
surface, and finally rupturing the outer laminæ of the tortoise-shell,
through that same force by which the tender radicle of a plant
penetrates very hard ground. As soon as the surface was once ruptured,
the shell of the Chelonobia, growing outwards and downwards, would
easily, like a wedge, turn up the laminæ of the tortoise-shell; and
their ragged ends would surround the Chelonobia, as is seen actually to
be the case. In the genus Coronula and its allies, which are attached
to Cetaceans, we shall presently see, that the epidermis immediately
under the downward growing shell, and apparently in consequence of the
pressure thus exerted, is thinner than in the surrounding parts. In
two specimens of _Chelonobia caretta_, imbedded much more deeply than
usual--in one of which half the basal edge of the shell had fairly cut
through the carapace, and in the other was on the point of effecting
this--the tortoise-shell manifestly thinned out towards the line of
yielding; now this, I suppose, must be attributed either to absorption,
or to the living tortoise-shell being actually stretched till rendered
transparent and ready to burst or until bursted. On the latter view
of the tortoise-shell having been stretched, we must further suppose
that the pressure has prevented fresh layers of tortoise-shell being
deposited under the old and yielding laminæ. In one of the above two
specimens, the walls of the Chelonobia were deeply folded, nevertheless
the laminæ of the tortoise-shell followed every curvature, showing
that, though now so rigid, during the slow imbedment of the Cirripede
it must have been sufficiently pliant. A shell attached, as these two
specimens were, could never be removed, and, whether dead or alive,
would remain for ever imbedded in the tortoise-shell. Dr. R. Ball,
of Dublin, informs me, that he has seen specimens in which the shell
of the cirripede not only had penetrated the carapace, but likewise
the underlying bone, and had even entered some way into the body of
the turtle: it is well known that the tusk of a boar or the horn of a
ruminant, when curving in abnormally, will sometimes penetrate deeply
into the bones of the face or head; and this, I believe, is effected,
not by the fracture of the bone, but by the absorption of the point
pressed on: I conceive a similar process must have taken place in the
curious specimens examined by Dr. Ball.
1. CHELONOBIA TESTUDINARIA. Pl. 14, fig. 1 _a_-1 _d_, fig. 5; Pl. 15,
fig. 1.
LEPAS TESTUDINARIA. _Linn._ Syst. Naturæ, 1767.
VERRUCA TESTUDINARIA. _Ellis._ Phil. Transact., vol. 50, 1758, Pl.
34, fig. 12.
BALANUS POLYTHALAMIUS. _Bock._ Naturforscher, Stuch. 12, 1778, fig. 9.
LEPAS TESTUDINARIA. _Poli._ Testacea Utriusque Siciliæ (1795) Tab.
5, fig. 9-11.
CORONULA TESTUDINARIA. _Ranzani._ Memoire di Storia Naturale, Decade
1, (1820).
---- ---- _De Blainville._ Dict. des Sciences Nat., (1824), Tab.
117, fig. 2.
CHELONOBIA SAVIGNII (?) _Leach._ Encyclop. Brit. Suppl., vol. 3, 1824.
ASTROLEPAS ROTUNDARIUS. _J. E. Gray._ Annals of Philosoph. (new
series), vol. 10, 1825.
_Shell conical, depressed, heavy: radii rather narrow, depressed,
generally notched on both sides._
_Hab._--Mediterranean; west coast of Africa; north-east coast of
Australia; Low Archipelago, Pacific Ocean; west coast of Mexico, 23°
N. Attached to turtles.
It is impossible to feel sure which of the three species of the genus
Linnæus had in view, when describing his _Lepas testudinaria_; but
as Spengler has well discriminated the following species under the
specific name of _caretta_,[123] and Ranzani the third species under
_patula_, the present name may, without question, be retained for the
following species. In several respects this species is intermediate
between _C. caretta_ and _patula_, but it can most conveniently be
described first.
[123] I am indebted to Dr. J. E. Gray for having guided me to this
identification.
_General Appearance._--Shell strong, globulo-conical, depressed;
outline broadly oval; surface smooth, generally well preserved, but
when disintegrated, upper part finely striated; colour dead white;
orifice oval elongated, rather exceeding in length one third of the
longer basal diameter of the shell. The radii are rather narrow, and
deeply depressed; they have their summits square: their outer lamina,
as explained under the genus, on both sides of each suture is in most
specimens divided into teeth, the points of which face and touch
each other. These teeth or notches give quite a peculiar appearance
to the shell, and alone suffice to discriminate this species; they
are sometimes blunt and partially obliterated, but it is rare to
find a specimen in which some few teeth do not occur in some one of
the six radii. I have, however, seen two or three specimens with all
six radii perfectly smooth; in one of these the general shape of the
shell, without the aid of any internal characters, almost sufficed
to show that it belonged to the present species; but in another
specimen, which had unusually narrow radii, and the whole surface of
which had undergone considerable disintegration, and was consequently
striated, could only be distinguished from _C. caretta_ by internal
characters. I have seen several specimens having very irregularly
shaped compartments, but generally the appearance of the whole shell
is highly symmetrical, like a star; and the genus was appropriately
named by old Klein, _Astrolepas_. In some specimens, in Mr. Cuming's
collection, from the Low Archipelago, in the Pacific, taken off the
toe-nail of a turtle, the shape was almost cylindrical; the shell
almost resembling that of _Coronula diadema_. The largest specimen
which I have seen was 2.3 of an inch in basal diameter, but only .55
in height.
_Structure of Shell and Radii._--After the full generic description,
the only point to which I need allude is, that the radiating,
parietal septa, as well as the descending sheath, are much thicker
than in _C. patula_, and that their basal edges can be plainly seen
by the naked eye to be dentated with numerous points. The thickness
of these plates and of the sheath varies considerably. In _C.
caretta_, I may add, the plates are broken up into many separate
points, and in this species the descending sheath is not generally
perforated, excepting at the sutures, by loop-holes for the entrance
of ribbons of corium. The sheath and inner lamina of the parietes
in _C. testudinaria_, taken together, fully equal one third of the
entire thickness of the walls. Flattened cavities or tubes run up
between the parietal septa for about two thirds of the height of the
inside of the shell. With respect to the radii, I have only to add,
that the thickness of the inner portion relatively to the generally
notched outer lamina, varies considerably.
_Opercular Valves_ (fig. 1 _b_-1 _d_).--These closely resemble
each other in all three species, and have been almost sufficiently
described under the genus. The scutum has its occludent margin always
sinuous, but to a variable degree. In one specimen there was a deep
little pit at the rostral end for the rostral depressor muscle. The
terga vary considerably in shape, according as the basi-carinal
corner is more or less truncated. The external furrow, marking the
position of the rudimentary spur, varies much in distinctness,
chiefly depending upon its nearness to the carinal margin of the
valve.
_Mouth and Cirri._--The labrum sometimes has its teeth worn away.
The second pair of cirri, relatively to the others, is shorter and
thicker than in the two following species.