Opisthobranch anatomy is largely the result of the process of torsion, a radical change in the organization of the body during development. The digestive system is characterized by a muscular buccal mass that contains the radula and labial cuticle (Figure).

The radula is a ribbon of chitinous teeth used to feed in different ways. It varies enormously between groups and is generally a good specific character of the species. The labial cuticle is a chitinous plate that sometimes has numerous jaw elements (Figure).

The buccal mass is normally connected to a pair of salivary glands and the esophagus, which in many groups has a crop with numerous chitinous plates (Figure).

Chitinous plates

The esophagus is connected to the intestine through the stomach, which is more or less dilated and to which the digestive gland is attached. In some groups, a cecum exists which connects to the esophagus and stomach. The circulatory system is open, like other mollusks, and blood movement is partially produced by a heart (consisting of two chambers) and the movement of the body.

The nervous system is composed of a ring of ganglia located around the anterior region of the esophagus attached by commissures and connective tissue.