Page:American Seashells (1954).djvu/34

 CHAPTER II

private lives of the snails, or gastropods as they are more correctly called, are almost as varied as the different kinds of seashells that are found along our beaches. More than half of the 80,000 species of existing snails live under marine conditions, the remainder being air-breathing land species or inhabitants of fresh water. In their evolutionary struggle for existence, they have shown an amazing diversity in adapting themselves to nearly every condition found in the sea. There are snails that creep, jump, swim, burrow, some that are permanently anchored to rocks and a few that live inside other marine creatures. In a few cases, as in some conchs and top shells (Trochus), the snail may play host to small fish and tiny crabs.

Gastropods have experimented in all manner of forms, colors and sizes. In size they vary from the two-foot-long Horse Conch of Florida (Pleuroploca gigantea) to the microscopic Vitrinellas that scarcely exceed the size of a grain of sugar. Some species display unusual ornamentation and, as in the Murex shells, produce long, delicate spines. There are few objects in nature that can vie in beauty with the glistening sheen found in the shells of the olives and cowries. On the other hand, the beautiful sea slugs or nudibranchs may entirely lack a shell. The Carrier Shell, Xenophora, has acquired the strange habit of collecting shells, bits of coral and other hard objects, and cementing them to its own shell.

WHERE THEY LIVE From the high levels of the coastal cliffs to the canyons of the ocean’s bottom, a thousand kinds of habitats have been adopted by marine gastro- 16