THE VIOLET SNAILS FAMILY IANTHINIDAE. Shell spiral, helicoid, fragile, semi-transparent, violet coloured, about 1 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 IANTHINA, Lam.
The Violet Snail (1. 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 6o The Violet Snails shoreward. It occasionally happens that a purple band is painted on the beach, the shattered fragments of purple shells. Even those which escape breaking by the surf are unable to get back to their element because the foot is not adapted to such effort. The sun kills them and birds devour them. It is generally
years before another school of Ianthina is wrecked on the same beach.
Violet snails are often met far off shore. But I fancy that only skilled observers would see the little fleet. The elongated raft is but a small group of bubbles on the surface. At one end of it the head and foot of the mollusk come nearly out of the water, but they look transparent. The mouth of the shell is turned upward, and the exposed outer whorl where the body lies is coloured a deep violet which blends with the deep blue of the sea. The apex is farther from the surface, and is a paler violet. The precious eggs are quite out of sight.
The chief enemies of the violet snail are sea birds that skim and scan the surface for food. Against them Nature has given this little creature adequate "protective coloration" to enable it to escape detection. It has no eyes, and the only defence it offers when disturbed is to exude a little cloud of violet ink.
For its food special provision is made. Small jelly-fishes which like the surface of the sea swarm in numbers so great that the violet snail has but to thrust out its prehensile proboscis to catch them.
Off our Florida coasts the genus Vellela abounds, each indivi dual a cake of jelly, bright blue, transparent, hung below with short streamers and above hoisting a three-cornered sail. This is a hydroid colony, like the Portuguese man-of-war. The violet snail seizes one with its snout, and tears it to shreds with its remarkably large rasping tongue. 1t is a surprise to see so delicate a mollusk tackling a "jelly-fish" four or five inches long, and well provided with protective stingers.
Barnacles, which attach themselves to its shell, are occasion ally eaten by lanthina. A blue crustacean lives on the float, asking nothing of its host but lodging and free transportation. Some contend that the young of the violet snail, as they hatch, get on the raft of their mother and secrete little floats before they are equipped for life in the water. This is doubtful, for each is born with a swimming apparatus.