The superfamily Aplysioidea is a superfamily of mostly rather large sea slugs, marine gastropod mollusks in the clade Aplysiomorpha within the informal group Opisthobranchia. This superfamily contains only one family, the Aplysiidae; the sea hares. These animals are commonly called sea hares because, unlike most sea slugs, they are often quite large, and when they are underwater, their rounded body shape and the long rhinophores on their heads mean that their overall shape resembles that of a sitting rabbit or hare.