Anatomical organization of opisthobranchs molluscs focuses on the process of detorsion. This process involves a radical change in the organization of the body during the development process.
The opisthobranchs’ digestive system is characterized by the presence of an oral muscular mass containing the radula and a labial armor. The radula is a chitinous teeth ribbon that is used for food in various ways. The shape or the radula varies greatly among opisthobranch species and it is generally a good distinctive character among species.
The buccal mass is normally connected to a pair of salivary glands and the esophagus. The esophagus in many opisthobranch groups has a bag with numerous chitinous plates. The esophagus is connected to the intestine through the stomach, which is a more or less extensive area which joins with the digestive gland. In some groups, there is a blind tract that connects the esophagus and the stomach.
The circulatory system of opisthobranchs molluscs is open, as in the rest of the molluscs, and the blood circulation is partly produced by a two-chamber heart and body movement.
The nervous system of opisthobranchs is composed by ganglia ring located around the anterior side of esophagus, joined together by connective tissue.