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.
All Bulla species have large, ovate, external shells, which are large enough to accommodate the whole snail when retracted. All species have rather similarly shaped shells, which have a deep, narrow umbilicus at the apex. No operculum is seen.

The smooth shell of Bulla spp. is ovate and expanded, with a deep, sunken involute top. Since little difference exists between the shells and in the morphology of the radular teeth, some uncertainty remains about the exact taxonomy of the species in Bulla.
These snails are mostly nocturnal and can be found on shallow, sandy coasts grazing among sea grasses, feeding primarily on green algae. They bury themselves in mud when the tide is out.