This small class of marine mollusks includes 200 species of burrowing animals commonly known as the tusk, or tooth, shells. The shell is long, cylindrical and tooth- or tusk-shaped, and open at both ends. The foot and the small head project from the larger end. Threadlike tentacles hang from the head and are used for gathering the microscopic organisms on which tusk shells feed. Most scaphopods are tiny, usually only several inches (about 6 cm) long. They are found in both shallow and deep waters; they burrow into the bottom, with only the upper opening protruding.