Originally placed in the Diaphanidae these were separated into their own family in 2015. They possess unique features including an internal shell and differences in the radula.
The shell is small, thin, opaque, sculptured and voluminous (globose). The whole animal is small, usually no more than 7 mm long. Although the shell is usually internal some species have a dorsal opening in the mantle allowing the shell to show through.
The head shield is indented forming rolled-up lobes at the anterior corners. The right side of the animal bears a conspicuous elongated appendage directed upwards and posteriorly that is acutely tapered.
The foot is broad anteriorly, elongated posteriorly and tapered. The gill is not visible externally.