Page:The Zoologist, 4th series, vol 3 (1899).djvu/556

526

the Superintendent of the Indian Museum, Calcutta, has just published, in the 'Journ. Asiat. Soc. Bengal,' a very interesting account of a new Hermit-Crab (Chlænopagurus andersoni) exhibiting adaptive commensalism with a Sea-Anemone. The Hermit-Crab is noteworthy (1) in having for its refuge, not the usual mollusc-shell, but a sheet or blanket formed by the cœnosarc of a colony of Sea-Anemones; (2) in being—as far as the male is concerned—symmetrical; aud (3) in having the appendages of the 3rd-5th somites of the male, and of the 2nd-5th segments of the female, present on the right or left side indifferently.

"There is nothing unusual in the fact that the protective covering of the abdomen is not a mollusc-shell, for in these seas alone there are several well-known instances of Hermit-Crabs making use of other convenient receptacles. For instance, Pylocheles miersi is found impacted in hollow twigs of sunken drift-wood; Troglopagurus, according to Messrs. Thurston and Henderson, lives in small cavities in coral; and I have myself seen a large Cœnobita, on the island of Minnikoy, holding the empty shell of a small coco-nut over its abdomen. Again, in other parts of the world, Gryllopagurus lives in burrows of its own construction; Pylocheles Agassizii was found concealed in a cavity in a piece of sandstone, and another specimen was taken from the gastral chamber of a siliceous sponge; Xylopagurus rectus, like our Pylocheles miersi, was discovered in a lodging in drift-wood; Ostraconotus and Tylaspis are both believed to have some special protective shield, other than a shell; and Porcellanopagurus lives free among seaweed.

"Again, the association of our new form of Hermit-Crab with a Sea-Anemone is nothing strange: indeed, commensalism between Crustacea and Sea-Anemones is one of the most familiar facts of zoology, and a large number of instances of it have been described. In most cases, however, the facts seem to be that an individual of a definite species of Crab and an individual of a definite species of Sea-Anemone have both at once taken possession of the same mollusc-shell, which they continue to inhabit for their mutual advantage,—the Crab acting as locomotive to the Sea-Anemone,