Trochidae (Top Shells)

Family: Trochidae (Top Shells)

Description: The top shell family is very large, with hundreds of species and many genera. Most show an iridescent interior, numerous whorls, and a horny operculum. Varying shell characteristics have led to specification of several distinctive subfamilies. For example, in the Monodontinae, the base is quite flattened, giving the appearance of an inverted top. In the Calliostominae, a large, rounded aperture opens more to the side and makes the base markedly less flat. In the subfamily, Angarinae, the final whorls become separated rather than remaining sutured, leading to a species rather atypical in appearance (see Angaria delphinus, below). A family of rather similar shells, also found in the Trochacea superfamily, is the Stomatellidae family. The latter shells show several similarities to the Calliostominae subfamily indicated below.; For information on body plan, reproduction and feeding habits, see the Haliotidae family. Like the Haliotidae and other members of the Archaeogastropoda order, the top shell molluscs are primitive grazers that feed by rasping algae and small detritus off rocky surfaces.