|The family Aplustridae
(also known as Hydatinidae) includes acteonoideans with thin, strongly
inflated shells with low spires. Sometimes referred to as "bubble shells," they have large parapodia, lack an
operculum and cannot withdraw completely into their shells. The genus Hydatina is
nocturnal while Micromelo is
diurnal. They feed on
polychaete worms. There are at least four species in Hawaii in two
genera (Hydatina and Micromelo).