The sea urchins belong to the class Echinoidea, ("echinus" in greek means "a hedgehog"). And if you have ever seen an urchin, you know how they got the name! They resemble a ball covered in long projecting spines, (seen here as the long greenish projections).

The spines attach to the skeleton by ball and socket joints and are controlled by special muscle fibers. The spines are used in protection from predators (some species secrete toxins from glands associated with their spines). But, the spines are also used for locomotion, food collection and for wedging the animal into crevices.

Between the spines you will find the pedicellaria (seen here as the transpartent projections with the three-sectioned top, and also the three purple structures arranged a little lower). Pedicellariae consist of 2 or 3 bony valves that move together and apart to act like jaws. The jaws work to remove parasites and other unwanted material from the urchin’s surface. Pedicellariae are also found in other Echinoids (sand dollars and heart urchins) as well as in seastars.