A big blunt slug in dark purple-black with bright yellow or orange edging, up to 10 cm (4 in) and heavy with it. The shell is still there, reduced to a thin plate inside the body, so what a diver sees is a moving lobe of color with no hard parts at all - and often only the furrow it left in the sand.
It eats other headshield slugs. Most of this family have given up the radula entirely, and instead of rasping they engulf: the front of the body opens, the prey is sucked in whole with a mouthful of sand, and digestion sorts it out afterward. Bubble snails, shell included, go down the same way.
Color in this species is unreliable enough to have caused decades of confusion, with dark, pale, striped and spotted forms described repeatedly under different names before genetics tied them together. It is a good reminder that in this group the reliable characters are internal, and that a photograph is a starting point rather than an identification.
- large heavy-bodied slug, dark purple-black with bright yellow or orange margins
- body swollen and blunt, with no external shell visible
- leaves a shallow furrow in the sand where it has passed
- length up to 10 cm
