Foreign Substances attached to Crabs

Abstract

IF, as Mr. Garstang seems to suppose, the presence of tunicates on a crab is to be regarded as a danger-signal to its enemies, then Hyas must belong equally to both his groups α and β. I have found simple tunicates (A. sordida) on two small specimens of H. coarctatus. In one example they almost completely hid, and several were larger than, the crab. I do not know if anyone has observed Hyas “dressing” itself with tunicates. I should think it was an operation of some difficulty, at least in the case of A. sordida, which adheres pretty tightly to stones and shells. It cannot be said to be brilliantly coloured, so that its assumption by Hyas might be regarded as only an adaptation for concealment, as in the case of Algæ—belonging, therefore, to group α. It seems to me, however, very doubtful whether a small Hyas would, even if it could, willingly burden itself with such a serious incubus as half a dozen tunicates. Probably their presence is in no way due to any act of the crab's.