CLASS GASTROPODA

The odd name "gastropod" means "stomach foot," and refers to the presence of a huge muscular "foot" in what is he belly region. Most familiar of the gastropods are snails and slugs (Order Pulmonata), but the largest group is the primarily marine Prosobranchia, to which belong some 30,000 species of abalone, limpets, cowries, and many of the "seashell" animals. Snails and slugs, which are largely terrestrial animals that breath with lungs or a lung-gill combination, contain about 7,000 species. The 3,000 species of sea slugs (Order Opisthobrancia) or nudibranchs, include some of the most graceful, delicate and gaudy of mollusks.

When a sea slug meets a sea slug coming through the sand... they generally avoid each other. The two species shown here, from coastal California, include a very colorful species at left, and a more somber, cryptically colored animal at right. The flowery mantles of these animals are actually exposed gills.

Gastropod classification is based on the position of respiratory organs, being at the front (Protobranchia), outside and back (Opisthobranchia), or inside, as lungs, of the body. Many species are commercially important as foods or collector's shells. Some, such as the tiny cone shells (genus Conus) contain extremely powerful toxins that may easily kill a human.