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.