This slug is thick, fleshy and slimy to touch. It is covered in blister-like protrusions and the exposed gills are grey to orange in colour. It is the largest nudibranch in NZ waters.

It is frequently found in the low tide zone, extending to 3 m and deeper. It is found under boulders on exposed to semi-exposed shores. Occasionally it can be found in rock pools or sitting on orange sponges.

It is a predator feeding primarily on sponges.

It lays a coiled ribbon of eggs on rocks.

NZ Coastal Marine Invertebrates; Vol 1.