The body of Gastropods is divided into a head, foot, and visceral mass. Gastropods have a shell, although some have lost their shells through evolution. Gastropods are subdivided by shell form, or the absence of a shell, internal anatomy, size and shape of tentacles, foot, and mantle, as well as type of breathing organ. Gastropods have an embryonic process known as torsion, which distinguishes them from other mollusks. One side of the visceral mass grows faster than the other, which causes the body to form the shape of a snailshell.
Torsion is evident in the helmetshell.
Slugs are snails that have evolved and lost their shells in order to be able to fit into smaller spaces. However, they are unable to survive without water, as snails do by crawling back into their shells and sealing the hole with their operculum. Gastropods have a radula which is used for moving food to the back of the mouth and cutting plant material. A few gastropods have evolved their radula to bore holes in the shell of other mollusks to get food. The radula of cone snails can fire poison darts at prey.