Part 27

BRYER’S NUT-CRAB.

The little specimens before us appear to belong to Ebalia Bryerii. It is porcellaneous white, tinged with pale scarlet. The little feet are painted scarlet on a white ground, especially the swollen-jointed claws, which are very gay, and under a lens show a marbled pattern of rich scarlet. This little Crab has an unique appearance, very attractive. Its motions are quick and sudden, mostly lateral, when alarmed; but it is habitually sluggish. Sometimes it appears to sham death; for if pushed, it at first tries to escape by running; but if the annoyance continues, it stiffens its limbs, and allows itself to be pushed without resistance; and when laid on its back in the water, will lie motionless for a minute or more, then suddenly turn over and crawl away.

Hosts of other things we capture in this summary sweeping of the sea-bottom, and by the time we have drifted down towards the Orestone, till we are close enough to make out the noble leaves of the tree-mallows that grow out of its rocky heights, we have accumulated a marvellous store,--almost enough, indeed, to set up a little provincial museum. Brittle-stars and urchins; cucumbers great and small; bivalve and univalve mollusks; swollen ascidians, smooth and warty; active, shuffling, sucking fishes; heaps of mossy Bryozoa; long bristling tufts of Hydroid zoophytes; naked worms, twining and writhing amidst the mass, gleaming in purple and pearl; sea-mice “armed in gold,” like Virgil’s Orion; tangled masses of Serpula-pipes, every one with its scarlet-crowned tenant; these, and multitudes of creatures besides, come up from the teeming sea-floor, and all at once claim our bewildered attention. And there is not one of the host that is not worthy of it; not one that would not be an eloquent witness of its Creator’s glory; but we must for the present neglect them all (not without hope of another meeting with some of them at least), in order to devote a few moments to one group of remarkable interest.

It is that unaccountable association of diverse and unrelated creatures, which, if we had not repeatedly seen it, we should not believe; the companionship of the Hermit-crab with the beautiful Cloak-anemone.

HERMIT-CRAB AND CLOAKLET.

Every one is familiar with that impudent and intrusive species of Hermit-crab, which, with its foxy-brown head and legs protruding, rolls over shells and pebbles with rattling patter, on almost every beach. The species I speak of is quite distinct from that homely and amusing subject. Though attaining a size fully equal, its proportions are much slenderer and more elegant; and the colours,--a light fawn, set off with soft tints of azure, lilac, and scarlet,--are far more beautiful than those of its fellow; not to speak of technical characters which abundantly distinguish the two.

The companion of the Cloaklet, which bears the name of Mr. Prideaux of Plymouth, who first made it known, is exclusively a deep-water species. Found on various parts of our coast, it invariably occurs in this association. I believe the Crab in no instance lives without the Anemone, the Anemone in no instance without the Crab. Examples, indeed, do now and then occur, as mentioned by Forbes, in which the one comes up in the dredge without the other; but I believe this is only when the rude action of the dredge has frightened the Crab, and induced it suddenly to vacate the shell and desert its friend. The Bernard is never attended by any such companion.

The history of the tenancy of univalve shells by these curious Crabs is well known; and the comic scenes that take place in the process of flitting from one tenement to another, larger and more commodious, have been so fully narrated by myself and other observers, that I shall assume the reader to be conversant with them. And the rather because the association of the Crab with the Zoophyte is a thing so much more singular, so much more unaccountable, and so much less generally known, that I shall seek to tell the story in some detail.

PLATE 27.

P. H. GOSSE, del. LEIGHTON, BROS.

PURPLE HERMIT-CRAB. CLOAKLET. COMMON HERMIT-CRAB. ]

HERMIT AND CLOAKLET.

To premise:--the Cloaklet is an anemone of the Sagartia family, beautiful in its colours and remarkable in its form. It is generally reddish-brown on the outer (lower) part of its body, which hue melts into snowy white on the upper parts; the whole studded with rosy-purple spots, and surmounted by a marginal line of pale scarlet. The tentacles and disk are pure white. It attains a rather large size, and has the peculiarity of being not round in its basal outline like other Anemones, but oblong, the base expanding in two lateral directions. It always selects the inner lip of an univalve shell for its place of adhesion, and the two lateral ends of its base gradually extend around the mouth of the shell till they meet on its outer edge, and unite with a suture: thus the outline of the animal forms a ring.

It had often been an interesting speculation with me, in what manner the due relation of size is maintained between the Adamsia and the shell, in the progressive growth of the former. There is a manifest proportion between the two, the young Cloaklet occupying a small shell, such as that of a Littorina or Trochus; the full-grown individual a large one, such as that of a Natica or Buccinum. The Crab is able to shift from a smaller to a larger shell when he needs enlarged accommodation; and since we know that his congener, P. Bernhardus, does this habitually, we naturally conclude that such is the habit of P. Prideauxii. Presuming then that this is the case, what becomes of the Adamsia? If the Crab shifts his quarters and leaves the Adamsia behind, the association is broken, and we should constantly find Paguri without Adamsiæ, and Adamsiæ without Paguri. But we find neither the one nor the other.

On the other hand, if Adamsia is able to shift its quarters also, how does it proceed in its search for a new shell? If it forsakes the old tenement at the same time as the Crab, and together with it takes possession of the new one, by what means is unity of will and action secured? What communication of thought takes place from the one to the other? As the Adamsia does not adhere to the Crab, but to the shell, that is, as they are independent of each other’s movements, who takes the initiative? Who goes to seek the lodging? And at what point of the transaction does the other come in? All these questions I had mused upon with interest; and at length received some light towards their solution.

On the 10th of January, 1859, I obtained, by dredging, in Torbay, a specimen of Adamsia palliata, about half-grown, on a rather small shell of Natica monilifera, tenanted by a Pagurus Prideauxii, which seemed already too big for his habitation. Having put them into a well-established tank of large dimensions, the contents of which were in excellent condition, I succeeded in doing what I had never done before, domiciliating both Crab and Adamsia. Both continued in the highest health, and became quite at home.

After about three months, however, I noticed that the Adamsia was not looking so well. One side or wing had gradually loosed its hold of the shell-lip, so that it hung loosely down beneath the breast of the Crab. Yet in other respects the zoophyte seemed healthy. Latterly, too, the Crab had manifested symptoms of uncomfortable straitness, in the great extrusion of his fore-parts; so great, indeed, as to expose even the front of the soft abdomen. Yet I felt reluctant to present to the Crab a larger shell, fearing that he would, in availing himself of it, desert his zoophyte friend, which would then die, and I should lose the specimen.

At length the desire to solve a problem in science prevailed over this feeling. A fact is better than a specimen. And so (on April 21st) I selected from my cabinet a full-grown Natica shell, and placed it on the tank-floor, not far from the disconsolate trio.

The Pagurus presently found the new shell, and immediately began to overhaul it. He did not do, however, as his brother Bernhard would have done, at once shift into the new house. Having turned it mouth upward, he took hold of the outer and inner lip, each with a claw, and began to drag it about the tank. Occasionally he relinquished the hold of one claw, and probed the interior in the usual manner, and then resumed his march. I watched the proceedings for an hour or more, when, having other work to do, I left him alone.

The thought did occur to me--Can this delay be intended to make the Adamsia cognizant of what is in contemplation, and to prepare it for the change? But I dismissed it as unlikely.

After about an hour’s absence I returned to the examination. The Pagurus was comfortably lodged in his new abode, and the old one, which now looked small indeed, lay deserted at some little distance. I eagerly turned the latter over, to see what was the condition of the Adamsia. Lo! no Adamsia was there; and the Pagurus, presently approaching the front of the tank, I saw, to my great gratification, that the old association was unbroken. There was the Adamsia, with one wing adhering to the lip of the new shell, and apparently the opposite wing also; but, from the position of the group, this I could not be quite certain of. The situation of the zoophyte was quite normal,--the centre immediately below the breast of the Crab, and in contact with the inner lip of the shell, while that wing which I could clearly see was creeping round upon the outer lip.

Examining now more closely the condition of things, with a lens, I saw that the central part of the Adamsia’s base was adherent by a small point of its surface to the under side of the thorax of the Crab, between the bases of the legs.

Now this adhesion to the Crab is a circumstance which, so far as I know, never takes place in the ordinary relations of the animals; and therefore I could not but think it an extraordinary and temporary provision for the removal of the Adamsia from the old to the new shell, and for the correct adjustment of its position on the latter.

How then can we avoid the conclusion, that, as soon as the Crab had found the new shell to be suitable for exchange, the Adamsia also was made cognizant of the same fact; and that, during the two hours which followed, the latter loosened its adhesion to the old shell, and, laying hold of the bosom of its protector, was by him carried to the new house, where immediately it began to secure the like hold to that which it had just relinquished?

Eleven days elapsed after the above observations were made, when I obtained another interesting fact bearing on this strange association. The Adamsia had not looked well since the change of residence; its adhesion to the shell had been but partial at the best, some days more, some days less, extensive; but for the most part a considerable portion of the zoophyte was hanging down from the shell. The Crab, on the other hand, was evidently in clover, and showed no inclination to go back to his old lodging.

On the 2d of May I found the Adamsia detached, and lying helpless on the bottom of the tank, beneath the Crab, who, when disturbed, walked off, leaving his companion behind. I thought now it was a gone case, and that it was all up with my elegant protegée.

An hour or two afterwards, however, how great was my surprise to see the Adamsia fairly established again, adhering to the shell by a good broad base, and looking more healthy than I had seen her for many a day! Strangely enough, she was adhering in a false position, having taken hold on the outer lip of the shell, instead of the inner, as usual. Here was a fresh proof of intelligence somewhere; and I at once set myself to find where.

Carefully taking up the shell with the aquarium-tongs, and bringing it close to the surface, but not out of water, I gently dislodged the Adamsia with my fingers, and allowed it to fall prone upon the bottom. I then released the shell with its tenant, and drove the latter towards the spot where the zoophyte lay.