Stiff Penshell (Atrina rigida)

SHELL LENGTH: Approximately 8 inches (20.32 cm)

Also called a Rigid Penshell, this large, fan-shaped bivalve has fewer than 20 ribs, some with large spines. The hinge side of this penshell is also straight with the other side being rounded. Although one of the largest shells on the beaches of the Carolinas growing up to ten inches in length, these fan-shaped mollusks are thin, brittle, and often broken. Penshells burrow and anchor themselves into sandy or muddy sediment with byssal threads where the top of the penshell stays above the surface to feed on particles in the water. The inside of the shell is smooth and shiny, often taking on a mother-of-pearl look. The outside is covered with spines, barnacles, oysters, slipper shells, and other animals that may find this habitat suitable. The adductor muscles actually bend the shells closed when they contract while relaxing the muscles causes them to spring back open. Penshell meat is edible, they produce a valuable pearl, and their byssal threads are woven in cloth in the Mediterranean. Commensal relationships exist with Tiny Oyster Crabs and small shrimp living in the protective mantle cavity feeding on excess food.