CHAPTER XXIX: THE VIOLET SNAILS 



Family Ianthinid.^ 



Shell spiral, helicoid, fragile, semi-transparent, violet- 

 coloured, about i^ inches in diameter; no operculum; head 

 prolonged into a large snout; radula very large; no eyes; ten- 

 tacles short; gill feather-like; foot small, attached to a gelatinous 

 float filled with air bubbles to which the egg capsules are attached. 

 Sexes separate. A pelagic family of gregarious habit found in 

 Atlantic and Pacific Oceans. One principal genus of three species. 



Genus lANTHINA, Lam. 



The Violet Snail (/. fragilis. Lam.) drifts in schools on 

 the ocean's surface. Let us look into the life history of this 

 delicate little sea snail. 



The strangest thing about it is a family trait. The foot 

 secretes a slimy substance which hardens in contact with water. 

 As it is excreted, bubbles of air are captured by the extensible 

 foot and imprisoned by the viscid exudation. So a series of 

 pneumatic cushions unite to form the flat raft. On the underside 

 of the float of the female the egg capsules are usually attached, 

 neatly ranked in rows. 



One by one the outermost capsules are ruptured and the little 

 snails tumble out to take their chances in the great ocean. The 

 raft is often found afloat without its mollusk. Storms wrench 

 many apart. Fish nip off portions of the float; the foot may 

 add more at the end next to the body. But a violet snail bereft 

 of its float drops to the bottom, and has no power to rise to the 

 surface. Moribund individuals let go their foothold on the raft, 

 and die on the ocean floor. But active individuals from which 

 the floats were cut loose by Mr. Arthur Adams reproduced them 

 in the aquarium when they were suspended by hooks in a position 

 just below the surface of the water. 



Unhappily, many an ill wind drives the lanthina swarm 



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