A bright green slug of about 3 cm (1.2 in) with four long finger-like lobes spread over its back and a small transparent shell sitting between them - an outline unlike anything else on the weed, and worth a photograph when found.
The lobes are defensive. Threatened, the animal waves them, and under real pressure it sheds them altogether; they continue to twitch while the slug retreats, and regrow later. Like its relatives it lives on Caulerpa, punctures the cells and drains them, keeping the chloroplasts for a time. The shell is too small to withdraw into and serves no protective purpose - it is a leftover from ancestors that had a full one, on its way out over evolutionary time. Calm shallow bays with standing Caulerpa are where to search, mostly after dark.
- four long finger-like lobes spread over the back
- small transparent shell between the lobes
- bright green with pale speckling
- on Caulerpa, never on coral
