Glimpses of Ocean Life; Or, Rock-Pools and the Lessons they Teach

by John Harper

The peculiarity, to which I alluded, of the Anomoura occupying shells that have formerly belonged to other animals, is so strange that some writers have not hesitated to express doubt upon the subject. This denial of a fact, which can so readily be proved, is one of the 'curiosities of literature.' Swammerdam, a Dutch naturalist contemptuously observes, 'What an idle fable that is which is established even among those who study shell-fishes, when they show some kind of the crab kind in their museums, adding at the same time, that they pass from one shell to another, devour the animals that lived in those shells, and keep them for their own habitations. They dignify them with the high-sounding names, and additions, as Soldiers, Hermits, and the like; and thus, having no experience, they commit gross errors, and deceive themselves, as well as others, with their idle imaginations.'

That there is nothing mythical in the matter can easily be made apparent to any person who chooses to visit the sea-shore. At such locality he need have no difficulty in recognising the Hermit-Crab, or meeting with numerous specimens for examination. Supposing such a one is at a rock-pool, and, moreover, that he knows by sight the Buckie (periwinkle), and Common Whelk, he will probably in such case be aware that the animals occupying these shells are snail-like in construction, and that their locomotion is consequently slow and formal. If, therefore, when peering into any pool he sees the Buckie, for instance, apparently change its nature, and instead of

'Dragging its slow length along,'

scamper off suddenly, or roll over and over from the top of an eminence to the bottom, he may rest assured that the original inhabitant has departed, and that its place is occupied by a Lobster-Crab.

The cause of his strange peculiarity I will briefly explain.

In the true Lobster the tail forms a most valuable appendage. In the tail the principal muscular power of the animal is seated; and by means of it, too, the animal is enabled to spring to a considerable distance, and also to swim through the water at will. This important organ is well protected by a casing consisting of a 'series of calcareous rings, forming a hard and insensible chain armour.'

In the Lobster-Crab there is no such arrangement. 'The abdominal segment of this singular animal, instead of possessing the same crustaceous covering as the rest of his body and claws, is quite soft, and merely enveloped in a thin skin. To protect this delicate member from the attacks of his voracious companions, the poor Pagurus is compelled to hunt about for some Univalve, such as a Whelk or Trochus, and having found this, he drops his tail within the aperture and hooks it firmly to the columella of the shell. Why Providence has doomed the poor Hermits to descend to such physical hypocrisy, and clothe themselves in the left-off garments of other animals, it is not easy to conjecture. No doubt, besides the defence of their otherwise unprotected bodies, he has some other object of importance in view. Perhaps they may accelerate the decomposition of the shells they inhabit, and cause them sooner to give way to the action of the atmosphere; and as all exuviæ may be termed nuisances and deformities, giving to these deserted mansions an appearance of renewed life and locomotion, removes them in some sort from the catalogue of blemishes.'

Professor Jones, when treating of this class of animals, forcibly remarks that 'the wonderful adaptation of all the limbs to a residence in such a dwelling, cannot fail to strike the most curious observer. The Chelæ, or large claws, differ remarkably in size, so that when the animal retires into its concealment, the smaller one may be entirely withdrawn, while the larger closes and guards the orifice. The two succeeding pairs of legs, unlike those of the Lobster, are of great size and strength, and instead of being terminated by pincers, end in strong-pointed levers, whereby the animal can not only crawl, but drag after it, its heavy habitation. Behind these locomotive legs are two feeble pairs, barely strong enough to enable the Soldier-Crab to shift his position in the shell he has chosen; and the false feet attached to the abdomen are even still more rudimentary in their development. But the most singularly altered portion of the skeleton is the fin of the tail, which here becomes transformed into a kind of holding apparatus by which the creature retains a firm grasp of the bottom of his residence.'

So great is the power of the animals to retain hold of their shell, and so intense their dislike to be forcibly ejected therefrom, that they will often allow their bodies to be pulled asunder, and sacrifice their life rather than submit to such indignity. This fact I have proved on sundry occasions. But supposing a crab to have taken a fancy to a shell, occupied by some brother Pagurus, (a circumstance of frequent occurrence), he quickly proceeds to dislodge the latter. Curious to state, this process never seems attended with any fatal result.