THE CRUSTACEA.
"Multa tamen lætus tristia pontus habet."
OVID.
The animals of this class, as regards organisation, must be placed
higher in the scale than the Arachnidæ, or spiders; but they are beneath
the Mollusca, although as regards affinity, the Mollusca in their lower
division--the Molluscoïda--more approximate to the Polyp class than to
the Crustacea.
The Crustacea is the highest division of articulate animals with feet;
they breathe by means of gills, and have no stigmata, or air-passages,
as in insects. The name signifies a hard crust or covering, with which
the animals are protected. This consists of layers of carbonate of lime
with one of pigment, generally, but not always, on the surface. The
general outline of these animals is peculiar; unlike insects, they are
not divisible into head, thorax, and abdomen; many species truly have no
head at all; but a pair of eyes point to the seat of intelligence. Most
of these animals have two compound eyes; but a few, like some insects,
have both simple and compound eyes. The mouth is situated in the under
part of the anterior of the body: in some cases they have jaws, as in
crabs; in others suckers only.
Passing over the vast numbers of beings which inhabit the debatable
ground--the _Annelids_, which were for ages confounded with the worms,
because of their resemblance in form:--a form which might be declared
forbidding, but, as Aristotle has well said, Nature, in her domain,
knows nothing low, nothing contemptible; the sea-leeches, whose
condition was an impenetrable mystery to Pliny, "Omnia incerta ratione,
et in naturæ majestate abdita;" and the singular cirripedes, one species
of which, the barnacle (_Anatifa lævis_), was thought by old Gerard,
the herbalist, and in his day by many others, to be the egg from which
the barnacle goose was produced--passing over these ocean tribes, we
reach the Crustaceans--the Insects of the Sea; of greater size, force,
and voracity than any land insect with which we are acquainted. They are
armed, also, at all points; for, in place of the coriaceous tunic, they
are clothed in calcareous armour, both hard and strong, and bristling
with coarse hairs, spiny tubercles, and even serrated spines.
The Crustaceans have nearly all of them claws, formidably hooked and
toothed, which they employ as pincers, both in offensive and defensive
war. They have been compared to the heavily-armed knights of the middle
ages--at once audacious and cruel; barbed in steel from head to foot,
with visor and corslet, arm-pieces and thigh-pieces--nothing, in fact,
is wanting to complete the resemblance.
These marine marauders live on the sea-coast, among the rocks, and near
the shore. Some few of them frequent the deep waters, others hide
themselves in the sand or under stones, while the common crab (_Carcinus
mœnas_, Leach) loves the shore almost as much as the salt water, and
establishes itself accordingly under some moist cliff overhanging the
sea, where it can enjoy both.
One of the necessary consequences of the condition of these animals,
enclosed in a hard shell, is their power of throwing it off. The
solidity of their calcareous carapace would effectually prevent their
growth, but at certain determinate periods Nature despoils the warrior
of his cuirass; the creature moults, and the calcareous crust falls off,
and leaves it with a thin, pale, and delicate tunic. In this state the
Crustacean is no longer worthy of its name--its skin has become as
vulnerable as that of the softest mollusc; but it has the instinct of
weakness--it retires into lonely places, and hides its shame in some
obscure crevice, until another vestment, more suitable for resistance,
and adapted to its increased size, has been restored.
The Crustacean has not a vertebral column. The covering of the
Crustacean consists of a great number of distinct pieces, connected
together by means of portions of the epidermis which have not yet become
hardened, in the same way as the bones in the skeleton of the vertebrata
are connected by cartilages, the ossification of which only takes place
in old age. The covering of the Crustacean consists of a series of rings
varying in number, the normal number of the body-segments being
twenty-one. Each ring is divisible into two arcs--one upper, or dorsal,
the other lower, or ventral; and each arc may present four elementary
pieces, two of which are united in the mesial line from the _tergum_, or
back; the lower arc is a counterpart of this, while the others form the
two side, or epimeral, pieces. The skin, therefore, performs the
functions of a skeleton, so that the Crustaceans, as was said by
Geoffroy Saint Hilaire, like the molluscs, live inside and not outside
the bony column. The analogue of the Crustacea amongst vertebrata is to
be found amongst Sturgeonidæ, whose hard, immovable bony case encloses a
softer skeleton; agreeing in its characters with that of the higher
divisions of vertebrata, although not possessing the solidity of bone.
The Crustaceans vary greatly in colour; some are of a dark, iron-grey,
with a dash of steel-blue, like metal weapons forged for combat; a few
of them are red, or reddish-brown; others are of an earthy yellow, or of
a livid blue.
"The integument," according to Milne Edwards, "consists of a _corium_,
or true skin, and epidermis, with a pigmentary matter, which colours the
latter. The corium is a thick, spongy, and vascular membrane, connected
with the serous substance which lines the parietal walls of the
cavities, as the serous membrane lines the internal cavities among the
vertebrata." This pigment is less a membrane than an amorphous matter
diffused through the outer layer of the superficial membrane, which
changes to red in the greater number of species in alcohol, ether,
acids, and water at 212° Fahr.
The calcareous crust of the animal is thick, and in the dorsal region
capable of great resistance; their members are also of remarkable
hardness; but in the smaller species the shell is often thin, and of
that crystalline transparency which permits of its digestion and
circulation being observed. Many species, which are quite microscopic,
contribute colour to the sea--red, purple, or scarlet: such are
_Grimothea D'Urvillei_ and _G. gregarea_.
Before the year 1823, it was not generally supposed that this class of
animals was subject to change of shape from the larva condition, and
during its progressive development; but about this time, and for some
years following, certain able microscopic experiments clearly
demonstrated that a minute nondescript kind of animal called the _Zoea
Taurus_, was nothing more nor less than the young of a kind of Prawn as
when extracted from the egg. Mr. Vaughan Thomson, by many successive
observations, and under the fire of much adverse criticism,
satisfactorily established the truth of metamorphic change in many
genera, and, in particular, in regard to the common crab (_Cancer
pagurus_); having succeeded in hatching the ova of this species, the
product of which were fine Zoeas. That there are variations in the
channel of this law of change has been admitted, but that generally a
metamorphosis exists, analogous to that of insects, in the various
genera of Crustacea, with hardly an exception, has been clearly
established.
[Illustration: Fig. 331. Zoea Taurus.]
The recorded observations of the eminent naturalist we have mentioned,
Mr. Thomson, as well as those of Mr. Couch, of Penzance, Mr. Milne
Edwards, and particularly those of the last mentioned, the learned
author of perhaps the best work extant on the Crustacea, are referred to
as treating most lucidly on this interesting subject.
As an illustration of this metamorphosis, we give figures of the _Zoea
Taurus_ in two states, viz., Fig. _a_, in the first stage; and second,
Fig. _b_, as the animal appeared on the fourth day after the first
microscopic examination, and when it resolved itself into a kind of
prawn. The drawings appear in Mr. Bell's "History of British Stalk-eyed
Crustacea," and were taken by that gentleman from the work of a Dutch
naturalist, named Slabber, who made the original observation in the year
1768, and published the result in 1778, from which time the subject had
been allowed to fall asleep until revived by Mr. Thomson.
Among the sea-spiders, which have no neck (_Cephalothorax_), the head
gradually disappears in the breast, but the belly remains distinct; the
middle of the body is compressed, the shape narrow and graceful. Among
the Crustaceans which have neither neck nor shape, the head, the breast,
and the belly form only one mass, often short, squat, athletic, and
difficult to take, as in _Pisa tetraodon_ (Fig. 332), the four-horned
spider-crab.
[Illustration: Fig. 332. Pisa tetraodon.]
Many of these animals have a powerful tail, consisting of a certain
number of ciliated paddles, which it uses in swimming to beat the water,
and to confuse its enemies.
The Crustaceans, so far as they are aquatic, respire by means of
_branchiæ_, or gills. In the larger species these branchiæ are
lamellous, or with filaments, whose supports are traversed by two
canals, one of which leads the blood into the general economy, the other
directs it towards the heart. These organs are enclosed in the body. In
the smaller species the branchiæ often appear exteriorly, hanging in the
water like a fungus. Sometimes these are at once swimming and breathing
organs; in other cases the animal has no special organs of respiration.
Nearly all the Crustaceans are strong, hardy, and destructive, forming a
horde of nocturnal brigands--merciless marauders, who recoil from no
trap in which they can lie in wait for their prey. They fight _à
l'outrance_ not only with their enemies, but often among themselves,
either for a prey or for a female, sometimes for the sake of the fight.
The miserable creatures struggle audaciously with their claws. The
carapace generally resists the most formidable blows; but the feet, the
tail, and, above all, the antennæ, suffer frightful mutilation. Happily
for the vanquished, the mutilated members sprout again after a few weeks
of repose. This is the reason for the many Crustaceans met with having
the talons of very unequal size: the smaller are those lost in battle
replaced. Nature has willed that the Crustacean should not long remain
an invalid. They soon return cured of their wounds. "We have seen
lobsters," says Moquin-Tandon, "which have in an unfortunate rencounter
lost a limb, sick and debilitated, reappear at the end of a few months
with a perfect limb, vigorous, and ready for service. O Nature, how thou
fillest our souls with astonishment and wonder!"
On the Spanish coast there is a species of crab, known, singularly
enough, by the name of _Boccaccio_; it is caught for its claw, which is
considered excellent eating. This is cut off, and the mutilated animal
is thrown into the sea, to be taken at some future time when the claw
has reappeared.
Crustaceans are nearly all carnivorous, and eat eagerly all other
animals, whether living or dead, fresh or decomposed. Little think they
of the quality or condition of their food. It is amusing to witness the
address and gravity with which the common crab, when it has seized an
unfortunate mussel, holds the valve open with one claw, while with the
other it rapidly detaches the animal, carrying each morsel to the mouth,
as one might do with the hand, until the shell is entirely empty. The
crab does not kill its prey directly, like the lobster; it is swallowed
also, but with greater appreciation.
M. Charles Lespés surprised upon the shore at Royan a shoal of crabs at
their repast. This day they seem to have dined in common, and "God knows
the enjoyment," as the good Fontaines said. They were in rows, every
head turned to the same side, and nearly on end on their eight feet.
They seized the small objects on the shore, which were carried to the
mouth, each hand in its turn in regular order: when the right hand
reached the mouth the left was on the ground. Let us just figure to
oneself a company of disciplined soldiers messing together at the same
table!
The Long-horned Corophius (_Corophium longicorne_), remarkable for its
long antennæ, knows perfectly well how to cut the byssus by which the
mussels suspend themselves, in order that the bivalve may fall on the
weeds among them. Other Crustaceans, also great oyster-eaters, have the
cunning or instinct to attack the mollusc without exposing themselves to
danger. When the bivalve half opens its shell to enjoy the rays of the
sun or take food, the evil-disposed Crustacean slips a stone between the
valve. This done, it devours the poor inhabitant of the shell at its
leisure.
The Corophius, respecting whom this question is hazarded, are extremely
numerous on the shores of the Atlantic towards the end of summer and
autumn. They make constant war upon certain marine worms. Off the coast
of La Rochelle they may be seen in myriads beating the muddy bottom with
their long antennæ in search of their prey. Sometimes they meet one of
these Nereida or Arenicola many times their own size, when they unite in
a body to attack it. In the oyster beds of La Rochelle they are useful
friends to the oyster by destroying these enemies, although they do not
hesitate to attack the mollusc when it comes in their way. During the
winter the mud of the bouchots gets piled up in unequal heaps, and when
the warm season returns, it has become hard and unfit for the
cultivation of the mollusc. It is necessary to level and dry these
mud-heaps--a process which would be both difficult and costly. Well, the
Corophia charge themselves with the task. They plough up annually many
square leagues covered with these heaps. They dilute the mud, which is
carried out by the ebbing tide, and the surface of the bay is left
smooth, as it was in the preceding autumn.
We have said that the Crustaceans do not even respect each other; the
larger of the same species often devour the smaller. _Rara concordia
fratrum!_ Mr. Rymer Jones relates that he had on one occasion introduced
six crabs (_Platycarcinus pagurus_) of different size into an aquarium.
One of them, venturing towards the middle of the reservoir, was
immediately accosted by another a little larger, which took it with its
claws as it might have taken a biscuit, and set about breaking its
shell, and so found a way to its flesh. It dug its crooked claws into it
with voluptuous enjoyment, appearing to pay no attention to the anger
and jealousy of another of its companions, which was still stronger and
as cruel, and advanced towards them. But, as Horace says--and he was not
the first to say it--"No one is altogether happy in this lower world":
"Nihil est ab omni parte beatum."
Our ferocious Crustacean quietly continued its repast, when its
companion seized it exactly as it had seized its prey, broke and tore it
in the same fashion, penetrating to its middle, and tearing out its
entrails in the same savage manner. In the mean time the victim,
singularly enough, did not disturb itself for an instant, but continued
to eat the first crab bit by bit, until it was itself entirely torn to
pieces by its own executioner--a remarkable instance at once of
insensibility to pain and of cruel infliction under the _lex talionis_.
To eat and to be eaten seems to be one of the great laws of Nature.
Though essentially carnivorous, the Crustaceans sometimes eat marine
vegetables. Many even seem to prefer fruit to animal food. Such is the
robber-crab (_Birgus latro_) of the Polynesian Isles, which feeds almost
exclusively on the cocoa-nut. This crab has thick and strong claws; the
others are comparatively slender and weak. At first glance it seems
impossible that it could penetrate a thick cocoa-nut surrounded by a
thick bed of fibre and protected by its strong shell; but M. Liesk has
often seen the operation. The crab begins by tearing off the fibre at
the extremity where the fruit is, always choosing the right end. When
this is removed, it strikes it with its great claws until it has made an
opening; then, by the aid of its slender claws, and by turning itself
round, it extracts the whole substance of the nut.
The Crustaceans have eyes of two kinds--simple and compound: the first
are sessile and immovable, and very convex; the other borne on a short
calcareous stem or peduncle, and formed of a number of small eyes
symmetrically agglomerated--the reunion of all the microscopic cornea of
a composite eye, resembling in shape a cap formed of facets. It is said,
for instance, that the eye of the lobster consists of 2500 of these
little facets. The simple eyes are _myopus_, or short-sighted--the
compound eyes for more distant but perfect sight. They appear to have a
strong sense of smell. Many of them cannot swim, but walk with more or
less facility at the bottom of the water. It is said, for instance, that
the cavalier of the Syrian coast, _Oxypoda cursor_ (Fabricius), is named
from the rapidity with which it traverses great distances.
Many systems have been proposed by different writers for the arrangement
of the Crustacea. That proposed by Mr. Milne Edwards recommends itself,
being founded on anatomical examination and actual experiment made by
himself and M. Audouin. He divides them into two great divisions: I.
Those in which the mouth is furnished with a certain number of organs
adapted for the prehension or division of food. II. Those in which the
mouth is surrounded by ambulatory extremities, the bases of which
perform the part of jaws. The first includes the MAXILOSA or
MANDIBULATA, again divided into _Decapoda_, having branchiæ attached to
the sides of the thorax, and enclosed in special cavities. The
_Decapoda_ are divided into: 1. BRACHYURA, namely, the Crabs. _Cancer_,
_Porlunus_, _Grapsus_, _Ocypode_, and _Doippe_, belong to this group. 2.
ANOMOURA, including _Droma_, _Pagurus_, _Porcellana_, and _Hippa_. 3.
MACROURA, including the Lobsters, _Astacus_, _Palæmon_, the Craw-fish,
_Palinurus_.
_Stomatopoda_, with external branchiæ, sometimes rudimentary, sometimes
none. Thoracic extremities prehensile, or for swimming generally, six or
eight pairs. This division includes Mysids, Phyllosoma, Squilla, &c.
The Cirripedia, or barnacles, are a very important division of
Crustacea; they are found in all seas, and attach themselves to almost
every object in the sea; from the immovable rock to the moving animal;
from the little Tunicata to the great turtle, or the whale.
The goose barnacles, _Anatifa_, have a flexible peduncle. The
Balanoidea, or sea acorns, like oysters, are rooted to the spot on which
they rest in their infant days; without the power, like the goose
barnacle, of swaying to and fro like a pendulum, be their resting-place
what it may.
One of the most remarkable animals of this class of Crustacea is the
_Limulus Moluccanus_--the Molucca crab. They are distinguished by a long
serrated spine, which looks most formidable. They are in great request
in the markets of Java. Linnæus thought that the fossil trilobites were
closely allied to the _Limulus_. Latreille, on the contrary, classed
them near the mollusc, chiton. The tail of _Limulus_ so strikingly
resembles that of many Trilobites, that the most common observers may
perceive an affinity.
CRABS AND CRAW-FISH.
Crabs and lobsters may be regarded as the chiefs or lords of the
Crustacean tribes. The crabs have very large claws and smooth backs; the
last have small claws and the back covered with spines. Tiberius Cæsar
had the face of a poor fisherman scratched by the rugged shell of a
craw-fish.
Lobsters, especially, have an amazing fecundity, and yield an immense
number of eggs, each female producing from 12,000 to 20,000 in the
season. The crab is also very prolific. These eggs are, in the lobster,
arranged in packets, which are attached to the lower surface of the
tail, to which they are connected by a viscous substance. The manner in
which the female lobster disposes of her burden is curious and
interesting. Whether she bends or stands erect she is able to hold it
obscurely or expose it to the light. Sometimes, according to Coste, the
eggs are left immovable, or simply submerged; at others they are
subjected to successive washings by gently agitating the false claw
which shelters them from right to left. When first exuded from the ovary
the eggs are very small, but they seem to increase during the time they
are borne about under the tail, and before they are committed to the
sand or water they have attained the size of small shot. The evolution
of the germ is in progress during six months. At the moment of exclusion
the female extends the tail, impresses upon the eggs an oscillating
motion, in order to destroy the shell and scatter the larvæ, delivering
herself in two or three days of her entire burden (Coste). "As the young
lie enclosed within the membrane of the egg," says Couch, "the claws are
folded on each other, and the tail is flexed on them as far as the
margin of the shield. The dorsal spine is bent backwards, and lies in
contact with the dorsal shield, for the young when it escapes from the
egg is quite soft; but it rapidly hardens and solidifies by the
deposition of calcareous matter on what may be called its skin."
[Illustration: Fig. 333. Palinurus vulgaris. _a_, left outward
jaw-foot.]
As soon as born, the young Crustaceans withdraw from the mother and
ascend to the surface of the water, in order to gain the open sea. They
swim in a circle; but this pelagic life is not of long duration; they
quit it after their fourth moult, which takes place between the
thirtieth and fortieth day, at which time they lose the transitory
organs of natation which they have hitherto possessed. After this they
are no longer able to maintain themselves on the surface, but drop to
the bottom. Henceforth they are condemned to remain there, and such
walking as they can exercise becomes their habitual mode of
progression. As they increase in size they gradually approach the
shore, which they had for the moment abandoned, and return to the places
inhabited by the parent Crustaceans.
The form of the larvæ differs so much from that of the adult, that it
would be difficult, except on the clearest evidence, to determine the
species from which they proceed. Former naturalists considered the
embryo cray-fish (_Palinurus_) to belong to a distinct genera, which
they designated _Phyllosoma_. It is now known, however, that these are
the young of the higher forms of Crustaceans undergoing metamorphosis.
In the various forms of _Macroura_ the metamorphosis is less decided
than in the _Brachyura_. In the fresh-water cray-fish no change whatever
takes place. Dissatisfied with the uncertainty of former experiments,
Mr. Couch undertook a series of observations, which are recorded in the
proceedings of the Cornwall Polytechnic Society, in which he established
the fact that metamorphosis takes place in the following genera: Cancer,
Xanthò, Plumnus, Carcinus, Portunus, Maja, Galathea, Hornarus, and
Palinurus. "Metamorphosis has been demonstrated," says Dr. Bell, "in no
less than seventeen genera of the Brachyurous order of Decapoda, in
which it is most decided and obvious; in Leptopodia, Majacea, Cancer,
Portunidæ, Pinnoteres, and Grapsus. In the Anomourous order it is seen
in the Pagurus, Porcellana, and Galathea; and in the Macrouran order in
Homarus, Palinurus, Palæmon, and Crangon."
[Illustration: Fig. 334. Portunus variegatus, male.
_a_, external antenna; _b_, external jaw-foot; _c_, tail or abdomen.]
The swimming of these creatures is produced by flexions and expansions
of the tail, and by repeated beating motions of the claws, the tail
acting as a sort of vibratile oar, aided by which they maintain
themselves in the water and facilitate their progress. As the shell
becomes more solid they get less active, and finally return to the
bottom to cast their shell and assume a new form.
According to the observations of M. Coste, the young lobster casts its
shell from eight to ten times in the first year, from five to seven in
the second, three to four times the third, and two or three times the
fourth year. In the fifth year they attain the adult state. Whence it
follows, that the small lobsters served at our tables have changed their
calcareous vestment something like twenty-one times, and are now clothed
in their twenty-second habit.
[Illustration: Fig. 335. Corystes Cassivelaunus, male.]
The crabs are numerous in species and various in size. The long-clawed
crab (_Corystes Cassivelaunus_) of Pennant and Leach (Fig. 335) is
remarkable for its long antennæ, which considerably exceed the body. The
jaw-feet have their third joint longer than the second, terminating in
an obtuse point, with a notch on its interior edge; eyes wide apart,
borne upon large peduncles, which are nearly cylindrical and short;
anterior feet large, equal, twice the length of the body, and nearly
cylindrical in the males; in the females (Fig. 336) about the length of
the body, and compressed, especially towards the hand-claw. The other
feet terminate in an elongated nail or claw, which is straight-pointed
and channeled longitudinally: carapace oblong-oval, terminating in a
rostrum anteriorly truncated and bordered posteriorly; the regions but
slightly indicated, with the exception of the cordian region, the
branchial or lateral regions being very much elongated.
[Illustration: Fig. 336. Corystes Cassivelaunus, female.]
Latreille gives the name of Corystes, which signifies a warrior armed,
to this genus of Crustaceans, from κόρυς, a helmet, but it is
perfectly inoffensive. Pennant had already conferred the name of
_Cassivelaunus_, the chief of the Ancient Britons, for the singular
reason, according to Gosse, that the carapace, which is marked by
wrinkles, bears, in old males especially, the strongest and most
ludicrous resemblance to the face of an ancient man. Pennant's
well-known sympathy with his British ancestry certainly never led him
to caricature the grand old British warrior, as Mr. Gosse surmises. On
the contrary, he saw in the Crustacean a creature armed at all points,
and he named it after the hero of his imagination.
In this species the surface of the carapace is somewhat granulous, with
two denticles between the eyes, and three sharp points directed forward
on each side. The male has only five abdominal pieces, but the vestiges
of the separation of the two others may be clearly remarked upon the
outer mediate or third piece, which is the largest of all. The length of
the antennæ is remarked on by Mr. Couch, in his Cornish Fauna. "These
organs," he says, "are of some use beyond their common office of
feelers; perhaps, as in some other Crustaceans, they assist in the
process of excavation; and, when soiled by labour, I have seen the crab
effect their cleaning by alternately bending the joints of their stalks,
which stand conveniently angular for the purpose. Each of the long
antennæ is thus drawn along the brush that fringes the internal face of
the other, until both are cleared of every particle that adhered to
them." On the other hand, Mr. Gosse suggests that the office of the
antennæ is to keep a passage open for ejecting the deteriorated water
after it has bathed and aerated the gills. "I have observed," he says,
"that, when kept in an aquarium, these crabs are fond of sitting bolt
upright, the antennæ placed close together, and pointing straight
upwards from the head. This is doubtless the attitude in which the
animal sits in its burrow, for the tips of the antennæ may often be seen
just projecting from the sand. When the chosen seat has happened to be
so close to the glass side of the tank as to bring the antennæ within
the range of a pocket lens, I have minutely investigated these organs
without disturbing the old warrior in his meditation. I saw on each
occasion that a strong current of water was continuously pouring up from
the points of the antennæ. Tracing this to its origin, it became evident
that it was produced by the rapid vibration of the foot-jaws drawing in
the surrounding water, and pouring it off upwards _between the united
antennæ_, as through a tube. Then, on examining these organs, I
perceived that the form and arrangement of their bristles did indeed
constitute each antennæ a semi-tube, so that when the pair were brought
face to face the tube was complete."
Among the numerous genera of _Brachyurous Crustaceans_, Grapsus is
distinguished by its less regularly quadrilateral form; the body nearly
always compressed, and the sternal plastron but little or not at all
curved backwards; the front strongly recurved, or, rather, bent
downwards; the orbits oval-shaped and of moderate size; the lateral
edges of the carapace slightly curving and trenchant; the ocular
pedicles large, but short: their insertion beneath the front and the
cornea occupies one-half of their length.
[Illustration: Fig. 337. Pagurus Bernhardus. 1, out of the shell; _a_,
right jaw-foot; _b_, in the shell.]
The Hermit or Soldier Crab (_Pagurus Bernhardus_, Fabricius, Fig. 337)
is, perhaps, the oddest and most curious of Crustaceans. It differs from
most other Crustaceans in this: in place of having the body protected by
a calcareous armour, more or less thick and solid, it has only a
cuirass and head-piece to protect the head and breast; all the rest of
the body is invested in a soft yielding skin; and this, the vulnerable
part of the hermit crab, is the delicate morsel devoured by the gourmet.
Nor is our somewhat evil-disposed Crustacean ignorant of the perfectly
weak and defenceless state of its posterior quarters. Prudence or
instinct makes it seek the shelter of some empty shell, of a shape and
size corresponding to its own. When it fails to find one empty, it does
not hesitate to attack some living testacean, which it kills without
pity or remorse, and takes possession of its habitation without other
form of process. Once master of the shell (Fig. 337), it introduces
itself, stern foremost, and installs itself as in an entrenchment, where
it is established so firmly that it moves about with it more or less
briskly, according to its comparative size.
The Pagurians belong to the Anomourous family of Crustaceans, of which
there are several genera, and a considerable number of species, the
animal economy of which has been ably commented upon by Mr. Broderip.
"Their backs," he says, "are towards the arch of the turbinated shell
occupied by them, and their well-armed nippers and first two pairs of
succeeding feet generally project beyond the mouth of it. The short feet
rest upon the polished surface of the columella, and the outer surface
of their termination, especially that of the first pair, is in some
species most admirably rough-shod, to give 'the soldier' a firm footing
when he makes his sortie, or to add to the resistance of the crustaceous
holders at the end of his abdomen, or tail, when he is attacked, and
wishes to withdraw into his castle. On passing the finger downwards over
the terminations of these feet, they feel smooth; but if the finger be
passed upwards, the roughness is instantly perceived. The same sort of
structure (it is as rough as a file) is to be seen in the smaller caudal
holders." In another species of Pagurus, from the Mauritius, which was
nearly a foot in length, he found a great number of transverse rows,
armed with acetabula, or suckers; these were visible without the aid of
a glass, which must very much assist the hold of the _Pagurus_.
During the feeding and breeding-time, the hermit throws out his head and
feet, and especially his great claws, and feels his way with his two
antennæ, which are long and slender. When he walks he hooks on with his
pincers to the nearest body, and draws his shell after him, as the snail
does his. But the undefended parts of the body always remain under
cover. At low water the hermits spread themselves over the rocky shore,
and the spectator thinks he sees a great number of shells which move in
all directions, with allurements different from that which belongs to
their essentially slow and measured race. If they are touched they stop
suddenly, and it is soon discovered that their shell is the dwelling of
a crustacean, not a mollusc. The animal lives alone in its little
citadel, like the hermit in his cell or the sentinel in his box. Hence
the name of _hermit_ and _soldier_.
When our crustacean outgrows its borrowed habitation, it sets out in
search of another shell, a little larger, and better suited for its
increased size.
The hermit often avails itself, as we have said, of empty shells
abandoned by their owners; when the tide retires these seldom fail them,
and the hermit may be seen examining, turning, and returning, and even
trying its new domicile. It glides slowly along on its abdomen, which is
large and somewhat distorted, sometimes in one shell, sometimes in
another, looking defiantly all round it, and returning very quickly to
its ancient lodging if the new one does not turn out to be perfectly
comfortable, often trying a great number, as a man might try many new
clothes before suiting himself. In its successive removals the little
sybarite chooses a hermitage more and more spacious, according to its
taste or caprice in colour or architecture. The cunning little creature
chooses its mansion, now grey or yellow, now red or brown, globular or
cylindrical, in the form of a spiral or of a tun, toothed or crenulate,
with trenchant edge or pointed terminations; but, as a rule, our
crustacean Diogenes houses itself in spirals of considerable length, as
in _Cerithium_, _Buccinum_, or _Murex_.
The hermit is very timid; at the least noise it shrinks into its shell
and squats itself, without motion, drawing in its smaller claws and
closing the door with its larger ones, the latter being often covered
with hairs, tubercles, or with teeth. In short, our prudent cenobite
clings so closely to the bottom of its retreat, that we might pull it to
pieces without getting it out entire; its tail is transformed into a
sort of sucker, by the aid of which it attaches itself firmly to the
walls of its habitation. It is at once strong and voracious, eating with
much relish the dead fishes and fragments of molluscs and annelids which
come in its way. Nor does it hesitate to attack and devour living
animals. When introduced into an aquarium, it has sometimes thrown it
into the utmost disorder by its insatiable rapacity. It has been
possible sometimes to preserve harmony among many individuals inhabiting
the same reservoir; but this has been owing rather to the impossibility
of their attacking each other, in consequence of cunningly-devised
barricades, than to their mildness of character or love of their
neighbour. These animals, in short, are very quarrelsome. Two hermits
cannot meet without showing hostility; each extends his long pincers,
and seems to try to touch the other, much as a spider does when it seeks
to seize a fly on its most vulnerable side; but each, finding the other
armed in proof, and perfectly protected, though eager to fight, usually
adopts the better part of valour, and prudently withdraws. They often
have true passages of arms, nevertheless, in which claws are spread out,
and displayed in the most threatening manner; the two adversaries
tumbling head over heels, and rolling one upon the other, but they get
more frightened than hurt. Nevertheless, Mr. Gosse once witnessed a
struggle which had a more tragic end. A hermit crab met a brother
Bernhard pleasantly lodged in a shell much more spacious than his own.
He seized it by the head with his powerful claws, tore it from its
asylum with the speed of lightning, and took its place not less
promptly, leaving the dispossessed unfortunate struggling on the sand in
convulsions of agony. "Our battles," says Charles Bonnet, "have rarely
such important objects in view: they fight each other for a house."
A pretty little zoophyte, the Cloak Anemone (_Adamsia palliata_), loves
to live with the hermit, and exhibits sympathies almost inexplicable. In
aquariums this anemone attaches itself almost always to the shell which
serves as the dwelling of the Crustacean; and it may be looked upon as
certain that where the hermit is there will the anemone be found. These
two creatures seem to live in perfect and intelligent harmony together,
for Mr. Gosse's observations establish the existence of a cordial and
reciprocal affection between them. This learned and intelligent observer
describes the proceedings of a hermit which required a new habitation;
he saw it detach, in the most deliberate but effective manner, its dear
companion, the anemone, from the old shell, transport it with every care
and precaution, and place it comfortably upon the new shell, and then
with its large pincers give to its well-beloved many little taps, as if
to fix it there the more quickly. Another species of Bernhardus makes a
companion of the _mantled anemone_. "And we are assured," says
Moquin-Tandon, "that when the crab dies its inconsolable friend is not
long in succumbing also."
"Is there not here much more than what our modern physiologists call
automatic movements, the results of reflex sensorial action?" says
Gosse. "The more I study the lower animals, the more firmly am I
persuaded of the existence in them of psychical faculties, such as
consciousness, intelligence, skill, and choice; and _that_ even in those
forms in which as yet no nervous centres have been detected."
LOBSTERS.
In a dietary, as well as commercial sense, the lobster far excels the
crab; like the latter, they have an amazing fecundity, each female
producing from twelve to twenty thousand eggs in a season; and wisely is
it so arranged, otherwise the consumption would soon exhaust them.
In France the size of the marketable lobster is regulated by law, and
fixed at twenty centimètres (eight inches) in length; all under that
size are contraband. Every year the inhabitants of Blainville proceed to
Chaussey to fish for lobsters. They are taken in baskets in the form of
a truncated cone, the mouth of which is so arranged that the animal can
enter, but cannot get out. The numbers caught by each fisherman and his
family in a season may be estimated at a thousand or twelve hundred,
which realise to the family thirteen or fourteen hundred francs, the
season lasting about nine months.
Lobsters are collected all round our own coast for the London market. On
the Scottish shore they are collected and kept in perforated chests
floating on the water, until they can be taken away to market. From the
Sutherland coast alone six to eight thousand lobsters are collected in a
season. This process goes on all round the coast, and as far as Norway,
whence an enormous supply of the finest lobsters are obtained, for which
something like £20,000 per annum is paid, all these contributions being
conveyed to the Thames and Mersey in welled vessels. But these
old-fashioned systems are being rapidly superseded by the construction
of artificial storing ponds, or basins. Of these ponds Mr. Richard
Scovell has erected one at Hamble, near Southampton, in which he can
store with ease fifty thousand lobsters, which will keep in good
condition for six weeks. Mr. Scovell's tank is supplied from the coasts
of France, Scotland, and Ireland, where fine lobsters abound. He employs
three large and well-appointed smacks, each of which can carry from five
thousand to ten thousand. On the coast of Ireland alone, it is said, ten
thousand fine lobsters a week might be taken.
The Lobster (_Homarus_) is found in great abundance all round our coast;
frequenting the more rocky shores and clear water, where it is of no
great depth, about the time of depositing its eggs. Various are the
modes in which they are taken; cone-shaped traps made of wicker-work,
and baited with garbage, are perhaps the most successful. These are sunk
among the rocks, and marked by buoys. Sometimes nets are sunk, baited by
the same material. In other places a wooden instrument, which acts like
a pair of tongs, is used for their capture.
Mr. Pennant, the naturalist, paid great attention to the lobsters, and
their habits are well described in a letter from Mr. Travis, of
Scarborough. "The larger ones," he says, "are in their best season from
the middle of October to the beginning of May. Many of the smaller ones,
and some few of the larger individuals, are good all the summer. If they
are four and a half inches long from the top of the head to the end of
the back shell, they are called sizeable lobsters; if under four inches,
they are esteemed half size, and two of them are reckoned for one of
size. Under four inches they are called pawks, and these are the best
summer lobsters. The pincers of one of the lobster's large claws are
furnished with knobs, while the other claw is always serrated. With the
former it keeps firm hold of the stalks of submarine plants; with the
latter it cuts and masticates its food very dexterously. The knobbed or
thumb claw, as the fishermen call it, is sometimes on the left,
sometimes on the right side, and it is more dangerous to be seized by
the serrated claw than the other."
There is little doubt that the lobsters cast their shell annually, but
the mode in which it is performed is not satisfactorily explained. It is
supposed that the old shell is cast, and that the animal retires to some
lurking-place till the new covering acquires consistence to contend with
his armour-clad congeners. Others contend that the process is one of
absorption, otherwise, if there were a period of moult, it would be
shown by their shells. The most probable conjecture is that the shell
sloughs off piecemeal, as it does in the cray-fish. The greatest mystery
of all, perhaps, is the process by which the lobster withdraws the
fleshy part of its claws from their calcareous covering. Fishermen say
the lobster pines before casting its shell, so as to permit of its
withdrawing its members from it.
The female lobster does not seem to cast her shell the same year in
which she deposits her ova, or, as the fishermen say, "is in berry."
When the ova first appear under the tail, they are small and very black,
but before they are ready for deposition they are almost as large as
ripe elderberries, and of a dark-brown colour. There does not seem to be
any particular season for this act, as females are found in berry at all
seasons, but more commonly in winter. In this state they are found to be
much exhausted, and by no means fit for the table.
[Illustration: Fig. 338. Nephrops Norvegicus.]
The generic name, _Astacus_ of Fabricius, is now confined to the
crawfishes, which have a depressed rostrum, one tooth on each side, and
the last ring of the thorax movable. The lobsters (_Homarus_) have the
eyes spherical, two rings of the thorax being soldered together. The
Norway Lobsters (_Nephrops Norvegicus_, Fig. 338) have the eyes uniform,
and the two last rings of the thorax movable.
The last is one of the most beautiful of the larger Macrourans. Its
general tint is pale flesh colour, with darker shades in parts, its
pubescence light brown. This is generally considered a northern species,
but Mr. Bell states that he has received specimens from the
Mediterranean. It is found plentifully on the coast of Norway, on the
Scottish coast, and in the Bay of Dublin. It is considered the most
delicate of all the Crustaceans.
[Illustration: Fig. 339. Crangon vulgaris, _a_, Anterior foot or claw.]
Before concluding this chapter, we perhaps should not omit brief notices
of the common prawn (_Palæmon serratus_) and the shrimp (_Crangon
vulgaris_), as types of an extensive variety of form of crustacea, which
inhabit all seas, and which perform important functions as regards the
sanitary state and economic condition of the waters of the ocean. These
small animals are the scavengers of the sea--they pick up and devour all
dead matter, leaving (it may be) a clean skeleton, without a shred of
fibre behind. In this respect they resemble the ants on land, doing
their work always thoroughly and effectively. We need hardly mention,
what is so well known to every reader, that prawns and shrimps are
amongst the most esteemed delicacies at our table, and as articles of
food occupy no mean place on the fish-stall. At Billingsgate alone, it
is hardly credible the immense quantities which arrive and are daily
consumed in the Metropolis by all classes of the community. The shrimp,
which although the smaller crustacean, is perhaps the finest flavoured
of the two, is sold in much larger quantities than its more aristocratic
congener, the prawn. The fishery of these savoury comestibles gives
occupation not only to regular able-bodied fishermen, who devote
themselves to this branch, but also to large numbers of women and
children, who--with their baskets and small nets--may be seen plying
their vocation in a multitude of well-known localities on our coasts,
especially on the southern and south-eastern shores. To the habitués of
Hastings, Southampton, Bognor, &c., there is not a more picturesque or
familiar marine picture than to behold a troop of little shrimpers, in
their grotesque and somewhat outré equipments, wading patiently knee
deep all in a row, as they push before them their pole nets.
Without giving a detailed technical and anatomical description, which
our space will not permit of, we may observe that the common prawn
(_Palæmon serratus_) is about four or five inches long, with a rounded
carapace, which is jointed and furnished at the head with numerous long
antennæ, the eyes being large and round. The tail is broad and flat, the
caudal laminæ of which are furnished with long hairs on the terminal
margins. The animal is also furnished with several pairs of feet, very
slender, and ordinarily bent within themselves.
The colour is light grey, spotted and lined with purplish shades. In the
water, however, prawns are almost transparent, from the nearly entire
absence of carbonate of lime in the carapace; they are thus very
beautiful objects in the marine aquarium, moving as they do like shadows
in the water.
When prawns are boiled, they become of a delicate pink colour, thus
adding beauty to the dainty morceaux.
Like most other kinds of crustacea, the prawn is much larger in tropical
climates. On the coast of South America, for instance, they attain a
size of nine or ten inches in length, three of them being considered
quite sufficient for a meal.
The London market is chiefly supplied with prawns from the Isle of Wight
and Hampshire coast.
Like the prawn, the shrimp has many varieties. The common shrimp
(_Crangon vulgaris_) is about two and a half inches long, from the eye
to the extremity of the tail. It is also furnished with a rounded
articulated carapace, with two antennæ. The eyes are prominent, marked,
and near each other; the tail flat, laminated, and hirsute. The shrimp
is not very unlike the prawn in general appearance, but is of a much
less complex and finished structure.
In colour it is greyish brown, clotted all over with dark brown. In this
species heat does not improve the colour.
This variety is one of the most abundant of all coast crustacea,
swimming about and laying on the sands (which they closely resemble in
colour) in immense shoals. Sometimes they are also found in deep water,
but the margin of the sea is their favourite habitat. It may be added,
that large quantities of the smaller palæmonidæ are caught with and sold
as shrimps. Shrimps are in spawn all the year through, and cast their
shells during the three months of spring.
The _Entomostraca_ of Milne Edwards, or the _Lophyropoda_ of Latreille,
have no suctorial mouth or mandibles capable of mastication; their
maxillæ are lamellose, and they have never more than ten swimming feet,
and have from one to two eyes on stalks, and live in fresh water. There
are two principal genera; the _Copepoda_ of Edwards, and the
_Ostracoda_. As a type of the first, we may mention _Cyclops vulgaris_
(Leach), which, true to its name, has but one eye. But the genus
_Pontia_ of the same family has two. As a type of the second order,
_Ostracoda_, we will specify the numerous family of the _Cyprides_,
whose animals are enclosed in a bivalve shell, which causes their
remains in Secondary strata to be classed with bivalve molluscs.