The sidegill slugs have a large plume-like gill located between the well developed foot and overlapping mantle, usually on the right side of the body

Medium or large oblong-shaped slugs which have two well developed cylindrical rhinophores on the head and two oral tentacles attached to either side of an oral veil.

The majority of families have an internal shell, others an external shell, and one family has even lost its shell completely

Notaspideans are exclusively carnivorous and utilize strong jaws and a broad radula to scrape tissue from their sponge or tunicate prey.

Photo : Berthellina martensis

Head partly concealed by the conspicuous mantle, which forms a skirt all around the body.

The skin is able to secrete strongly acid fluids on disturbance.

InternaI shell calcareous but fragile, usually unpigmented.

Photo : Berthellina sp

Body and mantle :

The mantle is relatively smooth, lacking pointed conical tubercles

Photo : B. martensis

Body and mantle :

The mantle is relatively smooth, lacking pointed conical tubercles

Photo : Berthellina sp

The mantle bears retractile conical tubercles; the rim is often emarginate posteriorly in life to form an exhalant respiratory siphon (indetectable after death) .