Final answer:
Tusk shells, or tooth shells, are named for their elongated, tubular shells that resemble tusks or teeth. Scaphopods have a radula and tentacles with bulbs for feeding and typically bury themselves in sand with the shell opening facing the water.
Step-by-step explanation:
Members of the class Scaphopoda, commonly known as tusk shells or tooth shells, are so named because of their unique shell shape. These marine mollusks possess elongated, tubular shells that resemble tusks or teeth, open at both ends. The front opening of these shells is always exposed to water, allowing the scaphopods to extend their tentacles to catch and manipulate prey. They utilize a specialized mouthpart called a radula for feeding, and their foot is adapted into tentacles with ciliated bulbs for capturing food. The scaphopod shell structure is notably different from that of other mollusk classes, such as the multi-plated chitons or the more diverse shelled forms found in gastropods.