Helmet Shells of the Cassidae Family

Three  Helmet Shells of the Cassidae Family can be found in this website:

Phylogeny: The Helmet Shells of the Cassidae Family are gastropod mollusks in the  Littorinimorpha order. This order is large and very diverse in shape including snail-like, cowry shaped, and limpet-like. Most are marine species but some are found in freshwater or on land. They all have a twisted shell and a muscular foot that is used for movement. The key characteristic is that they all exhibit torsion, which is a process where the body twists so that the anus, gills, mantle cavity, and reproductive organs all point forward. There are sixteen superfamilies in this large order. The Cassidae Family is one of nine families in the superfamily Tonnoidea. There are two subfamilies in this family – Cassinae with eight genera and thirty-eight species, and Phaliidae with five genera and sixty-five species. Shells in this family are also commonly called Cassids.

Description: The Cassidae Family includes both Bonnet Shells and Helmet Shells. They are medium to large, thick, heavy shells, with large body whorls. They are cylindrical to globose in shape, with low spires. They may be sculpted with spiral striae, cords, or knobs, or they may have a cancellate pattern caused by axial ribs crossing spiral grooves. Some species display varices. The aperture may be slit-like or crescent-shaped. They have an open, curved siphonal canal. The outer lip is thick, recurved, and sculpted with small to large teeth. The inner lip usually shows heavy callus and may be marked with grooves. The operculum is small and thin. The periostracum is either absent or thin. The largest species in this family reach 39 cm (15.3 inches) in length, though some sources extend this length to 41 cm (16.1 inches).

Habitat and Distribution: Helmet Shells are found on both sandy and hard substrates. They live intertidally and to depths of 4,660 m (15,285 feet). They are found worldwide, in temperate to tropical seas. At least nine species from the Cassidae Family found in Mexican waters.

Natural History: Helmet Shells bury themselves in sand substrate during the day and emerge at night as predators feeding on echinoderms, such as sea stars and sea urchins. The use their heavy shells to pin prey in place. They envelope the prey with their foot and mantle and then excrete an enzyme that paralyzes the animal. With urchins, they use their radula to penetrate the urchins test and then secrete toxins. In turn smaller Helmet Shells are preyed upon by crabs, fish, and predatory mollusks. They are gonochoric and reproduce sexually, with either internal or indirect fertilization. The eggs are laid as masses of  small horny capsules, forming irregular or cylindrical, tower-like structures. Each capsule contains hundreds of eggs, most of which will serve as food for the developing embryos. Helmet Shells are edible are are sought by fisheries and shell collectors.  The thick, colorful, Helmet Shells have been used since the 1500’s to make cameo jewelry.