Fig. 103.—The Cloak Anemone (Adamsia palliata) on a Whelk Shell, with Hermit Crab
The peculiar habit of the anemone just referred to makes it an interesting pet for the aquarium, for if removed from its natural home, and placed in the aquarium with a hermit crab, it will, sooner or later, as the opportunity occurs, glide from its hole on the stone or rock, and transfer itself to its favourite moving home.
It may be difficult at first to see what advantage can accrue to the anemone by the selection of such a situation; and, moreover, it becomes an interesting question as to whether the advantage is a mutual one. Close observations may, and already have, thrown some light on this matter, though it is probable that there still remains something to be learnt concerning the relations which exist between the inside and outside occupants of the portable house.
It may be noticed that the anemone almost invariably takes up a position on the same portion of the shell, and that, when fully expanded, its mouth is usually turned towards that of the crab. This seems to be a very favourable position for the anemone, since it is one that will enable it to catch the waste morsels from the crab’s jaws by its expanded tentacles. But it is, perhaps, not so easy to suggest a means by which the anemone can make an adequate return for free board thus obtained. It is well to remember, however, that crabs are regarded as such delicate morsels by fishes that we have already spoken of the value of these crustaceans as bait; while the fact that sea anemones remain perfectly unmolested in rock pools inhabited by most voracious fishes, coupled with the fisherman’s experience as to the absolute worthlessness of anemones as bait, is sufficient in itself to justify the conclusion that these creatures are very distasteful to fishes. This being the case, it is possible that the hermit crab is amply repaid by the anemone for its liberal board not only by partially hiding the crab from the view of its enemies, and thereby rendering it less conspicuous, but also by associating its own distasteful substance with that which would otherwise be eagerly devoured.
When the hermit grows too large to live comfortably in its shell, a change of home becomes necessary, and it is interesting to observe that the anemone living on the outside of the shell transfers itself at the same time; and this is a matter of vital importance to the crab, since it usually changes its lodging at the moulting period, at which time its body is covered by a soft skin, and is then even more acceptable as prey to the fishes. Thus the anemone accompanies its host, affording it continued protection during the period of its greatest danger.
Before leaving the cœlenterates we must refer to one other form which, though not often having its habitat between the tide-marks, is nevertheless a very common object in the neighbourhood of fishing villages, where the refuse from the nets used in deep water has been thrown on the beach. We refer to the peculiar animal known to fishermen as ‘Dead Men’s Fingers,’ and to the naturalist as the Alcyonium.
When seen out of water it is not by any means an inviting object, but is apparently a mass of gristly matter, of a dirty yellowish or brownish colour, sometimes flattened and shapeless, and sometimes lobed in such a manner as to suggest the popular name so commonly applied. It is always attached to some hard object, such as a stone or a shell, and is so frequently associated with oyster shells that it is by no means an uncommon object in the fishmonger’s shop, from which we have often obtained live specimens for the aquarium.
When placed in sea water it gradually imbibes the fluid surrounding it, becoming much swollen. Then little star-like openings appear, the circumference of each of which protrudes so as to form a little projecting tube. Finally, a crown of eight little tentacles is protruded, and the mass, so uninteresting at first sight, reveals itself as a colony of pretty polyps.