Bulla is a genus of medium to large hermaphrodite sea snails, shelled marine opisthobranch gastropod molluscs. These herbivorous snails are in the suborder Cephalaspidea, headshield slugs, and the order Opisthobranchia. These snails are popularly known as "bubble snails", and their shells as "bubble shells", because the shell of some of the species is very inflated indeed, almost spherical in shape, and is also very thin and light. According to some experts, Bulla is currently the only genus in the family Bullidae, which in turn is the only member of the superfamily Bulloidea.