Growing up to 12″ or 300mm, the Dolabella auricularia is one of the largest slugs in Hawaii (the Aplysia Argus can grow to a similar size).  On the reef it is easily mistaken for a large sponge.  Its most prominent feature is its blunt, cut-off  is often found on beaches or floating across the sand, dead — at least I’ve seen it dead more often than alive!  The animal documented here was a dark brown/black, but they can be red, yellowish-green, light brown, pinkish, etc. Like most sea hares, they can release purple ink when threatened and lay a spaghetti-like egg mass.  For more information and photos of more colourful animals, please see Sea Slugs of Hawaii.