This distinctive sacoglossan slug is green in colour, with black-tipped rhinophores and a single black margin along its edge (parapodia). It often has whitish papillae, although the density can vary considerably. It has quite large parapodia, which allow it to "swim", and it can be found drifting higher than usual in the water column. Also possibly found in South Australia, Elysia tomentosus is a very similar species, but differs by being more papillose, giving it a hairy appearance, and it has a pinkish parapodial margin, which has a black line on either side, giving it the appearance of having a double-lined black margin, instead of E. expansa's single black line.
