|The family Juliidae
includes the "bivalved snails"--unique among gastropod mollusks in
having clam-like shells into which the body can be withdrawn. They
were first described as bivalves from fossil material and only
recognized as gastropods when living animals were discovered in
1959. Diurnally active, they feed on algae of the genus Caulerpa. Some are among
the few gastropods to have green shells. At
least seven species are known from Hawaii in at least two genera (Berthelinia and Julia).