These species are most unusual in possessing a two-valved shell (two articulating valves like a scallop or clam) into which the animal can completely withdraw.
They are an example of convergent evolution being the only sea slugs, or even gastropod with a bivalved presentation (Commonly known as the bivalved gastropod).
During metamorphosis the sinistrally coiled veliger (larva) shell develops a visor that initially forms a fold but eventually grows into two halves. When crawling, the animal is twice the length of its shell, much of that length being its long and slender neck. The pointed tail however does not extend past the rear of the shell. Juliids are usually pale to dark green in colour. There is a pair of rounded oral lobes beside the mouth.
The rhinophores are auriculate, usually hollow-cylindrical and joined at the base, with the eye spots located immediately behind them on the neck. The gills are not visible externally.
They feed upon green algae belonging to the genus Caulerpa and are cryptic in situ, often only being observed when moving.