There is a small flattened internal shell which looks whitish when viewed through the translucent tissue, and there are dark spots visible through the dorsal surface which are the digestive glands.

[3] Another similar species is Berthella stellata, but that is rather smaller, transparent or whitish, and has a star-shaped opaque pattern in the centre of its back.

[4] Berthellina edwardsii feeds largely on sponges and tunicates, rasping the surface with the fine teeth on its radula.

Each individual is a hermaphrodite, and a pair of slugs will orientate themselves so that their genital openings are close together, and exchange sperm.

The eggs are numerous but tiny, and are laid in a whitish, coiled cylindrical, jelly-like ribbon, stuck to the substrate.