Page:The Zoologist, 1st series, vol 1 (1843).djvu/232

204 former species. From a small specimen which came with the others, this coral, in the young state, has a narrow base formed on a straight tube.

I have not seen either of these kinds of coral shaped like other Cyathophyllæ, with a conical tapering stem, yet from the shape of the star they are evidently allied to that genus, so that perhaps they may belong to the next class of instances, in which the coral or coralloid body is evidently modified by the parasitic animals which form a chamber in its substance, yet take a peculiar form, and appear never to be found except in conjunction with the parasite.

A very common instance of this kind is often to be observed on our own coast. Many of the shells taken possession of by the common hermit crab, are covered with a species of Alcyonium, described by Dr. Johnston of Berwick under the name of Alcyonium echinatum. This Alcyonium gradually enlarges, and being moulded on the body of the hermit crab, forms for that animal a house, adapted to its growth, so that it has no necessity either to enlarge its house by the absorption of part of the cavity of the shell which it inhabits, or by leaving the shell and seeking for another better adapted to its size, as other specimens are obliged to do which have not the assistance of the coral. One can understand that the crab may have the instinct to search for shells on which the coral has begun to grow j but this will scarcely explain why we never find the coral except on shells in which hermit crabs have taken up their residence.

The "calthrops shell," as it has been called (Turbo madreporoides, Burrows' 'Elements of Conchology,' t. 27, f. 1), is a shell inhabited by a Pagurus, which is covered by a peculiar species of cellepore. Another shell, similarly covered with another species of cellepore, is figured by Lister, (Conch, t. 585, lower right hand figure). Both the Cellepora Calthrops and C. Listeri above cited, are peculiar for having the mass of the coral marked with large green spots: and I have several other examples of the same kind from different parts of the world, two species of shells from the Chinese seas, covered with an Alcyonium, each with branching arms, the arms of the two specimens taking different and definite directions. Another, which appears to be very common on the west coast of Africa, is covered with a Lobularia? with large polypes, all the specimens having four large thick claw-like branches, bending down towards the mouth of the cavity which is inhabited by the Pagurus.

The Mollusca and Annelides which live in coral, equally cause the coral animals to protect them; some, as the Modiolæ, being sunk into