Prasinidae Stoliczka, 1871 (Prasinidae is a senior, but unused, synonym of Juliidae) Juliidae, common name the bivalved gastropods, is a family of small sea snails, marine gastropod mollusks or micromollusks in the superfamily Oxynooidea, an opisthobranch group.

He considered it a bivalve with similarities to Vulsella, Pedum, and Veneridae, but noted that it was difficult to classify due to its distinctiveness.

Crosse initially only had a single valve to study, and thus was unaware of its bivalved nature, and identified it as a gastropod similar to Hipponix.

The first-discovered live species of bivalved gastropod was Tamanovalva limax, described by Kawaguti & Baba (1959).

As Tryon (1884)[4] wrote in his description of the genus Julia: the shell is oblong, thick, and cordiform.

In two species [1] and [2] the camouflage is even more complete: the mantle of the animal is patterned in a way that closely resembles the structure of the alga on which it lives.

The species Julia zebra has shells that are finely striped with brown and blotched with white.

[11] After hatching, the juvenile snails immediately take their place on algae (the larval phase of veliger is extremely short).

Based on a classification by Jensen (1996),[17] three recent genera were recognized in the family Juliidae:[18] Julia Gould, 1862; Berthelinia Crosse, 1875; Tamanovalva Kawaguti & Baba, 1959.

subfamily The earliest known fossils of Juliidae date to the Eocene, though the group may have originated earlier, in the Paleocene.

The earliest-appearing genera are Berthelinia, Gougerotia, Hemiplicatula, and Saintia, which are known from the Ypresian age (56–48.07 million years ago) of the Paris Basin.