The members of this family possess a shell, oval in shape, but it is reduced and thin covering the viscera only. Parts of the shell are visible externally but the animal is unable to contract inside. The colours range from pale green to dark brownish green, often with spots, sometimes with reticulations.
The rhinophores are auriculate and the eye spots are distinctive on the sides of the neck just behind the rhinophores. Parapodia rise up from the lower sides of the body to cover, or partly cover, the shell. These parapodia most usually lie against the shell and exhibit papillae on the outer face in the genus Oxynoe. In the genus Lobiger each parapodium gives rise to two, large, elongate lobes that can be held erect with the outer face of each being papillose. The gills are not visible externally.
All possess a long and thick tail, that is at times, used in an attempt at swimming to effect an escape. The tail and larger of the parapodial lobes can be autotomized to distract a predator.
They feed on green algae belonging to the genus Caulerpa and are very cryptic in situ.