Scotch Bonnet Snail

The egg-shaped shell of this species usually grows to 40–55 mm in length (1 1/2" - 2 1/8") (the maximum recorded shell length is 121 mm (4.76 in)). It is thick and solid, with a moderately high spire and rounded body whorl, and adult specimens have approximately five whorls. The protoconch is rounded, colored cream with an orange to brown apex. The teleoconch is sculptured by spiral grooves crossed by mostly rather faint growth lines. Its surface varies in the degree of shell sculpture that is present. Some shells are completely smooth with a high gloss, whereas other shells are grooved. The surface of some shells is granulated, and some even have nodules on the shoulders of the whorls. Several times at different growth stages, the shell develops a thick outer lip, which is characteristic of the subfamily Cassinae.

There are published records of the nominate subspecies Semicassis granulata granulata from several warm-water and tropical areas of the Western Atlantic Ocean. It is considered the most common species of Cassinae in North America. Regions and countries where this species occurs include the East Coast of the US, in North Carolina, South Carolina, Georgia and Florida (East Florida, West Florida, and the Florida Keys). It has also been recorded on the Gulf Coast of the US, including Louisiana and Texas. The species is known to occur in the Caribbean Coast of Central America, including Mexico (Quintana Roo), Nicaragua, Costa Rica, Panama and Colombia, as well as Venezuela (Gulf of Venezuela, Carabobo, Sucre, Isla Margarita and Los Testigos Islands).

The Scotch bonnet is preyed upon by vertebrates, such as fish, and invertebrates, including crabs such as the blue crab and the Florida stone crab. Crabs can crush the snail's shell, eating the soft internal organs and muscle tissue. The snail's only defense mechanism against predation is to draw its body into the shell. By doing so, they can at least partially close the aperture using the operculum.

Scotch bonnets are predators; they search for their food on sandy stretches of the ocean floor, where they consume echinoderms such as sand dollars, sea biscuits, and other sea urchins (such as Echinocardium cordatum), drilling into their tests with the aid of sulfuric acid.

During the spring, favorable food supplies, adequate light, and optimum water temperature provide conditions for breeding and early growth. At this time, the female deposits hundreds of egg capsules in tower-shaped structures about 4 to 5 inches (10 to 13 cm) high. The male fertilizes these eggs. After fertilization, the eggs develop into trochophore larvae, and the eggs subsequently hatch as free swimming microscopic veliger larvae, which can be carried some distance on ocean currents.

In 1965, the US state of North Carolina named the Scotch bonnet as its official state shell, in honor of the abundance of Scottish settlers that founded the state. With this designation, North Carolina became the first state in the US to have a state shell.

Populations of S. granulata have been suffering a decline due to increased collection and accidental harvesting by commercial fishermen.