What does a keyhole sea biscuit look like?

A keyhole sea biscuit, also known as a keyhole urchin, features a flattened, disc-shaped body with a tough, rigid exterior. Its surface is typically covered in spines and has a distinctive star-shaped pattern, which gives it a unique appearance. The underside has a keyhole-like opening, where the mouth is located, surrounded by tube feet that help with movement and feeding. These creatures are usually found in shallow marine environments, often buried in sand or gravel.