|The family Hexabranchidae
includes flattened species with an inrolled mantle margin that can be
"unfurled" for display and swimming. There are two flattened, lobate
oral tentacles and the gills cannot be retracted into pockets. Among
the world's largest nudibranchs, they are nocturnal sponge feeders. Two
probable species are known from Hawaii in one genus (Hexabranchus).
Although this family had long been placed with the cryptobranch dorids,
recent work (Valdez, 2002a) suggests that it should be placed with