page_title: Juliidae
section_title: Description
hierarchical_section_title: Juliidae / Description
caption_attribution_description: English: drawing of the shell of Julia borbonica
context_page_description: Juliidae, common name the bivalved gastropods, is a family of minute sea snails, marine gastropod mollusks or micromollusks in the superfamily Oxynooidea, an opisthobranch group. These are sacoglossan sea snails, and many of them are green in color.
  These snails are extremely unusual in that their shells consist of two separate hinged pieces or valves. The valves are joined by a ligament, and look nothing like a normal snail shell; instead the valves look almost exactly like the two hinged valves of a clam, a bivalve mollusk, which is a related but very different class of mollusks.
  Up until the mid-20th century, the Juliidae were known only from fossil shells, and not surprisingly, these fossils were interpreted as being the shells of bivalves. Julia, which is the type genus of the family, was named in 1862 by Augustus Addison Gould, who described it as a bivalve genus. Julliidae are known from the Eocene period to the Recent, but they probably first appeared during the Paleocene.
context_section_description: As Tryon (1884) wrote in his description of the genus Julia: the shell is oblong, thick, and cordiform. The valves are closed, the margins entire and the valves are inequilateral. The lunule is deep circular, projecting into the interior of the right valve, the left valve is in the same place furnished with dentiform tubercles. The hinge line is simple and arched. The ligament is external and narrow. There are two muscle scars which are unequal and subcentral.
  These animals have two valves, and the soft parts can be completely withdrawn inside the shell. The two valves are usually thin and translucent.
  In the genus Tamanovalva there is a protoconch on the apex of the left valve. This is clearly visible in the left valve of Tamanovalva babai.
  The body of the live animals is in most cases green (as it is in many sacoglossans), and in many species the individual appears green in totality. This, combined with the very small overall size, makes the animal hard to see on the green algae on which it lives. This ability serves as crypsis, especially as cryptic coloration (camouflage). In two species  and  the camouflage is even more complete: the mantle of the animal is patterned in a way that very closely resembles the structure of the alga on which it lives.
  The empty valves of the shells of these animals are in some cases green, in other cases brownish-green or yellow, and in yet others, colorless. The species Julia zebra has shells that are finely striped with brown and blotched with white.
caption: Drawing of the interior of the left valve of the shell of "Julia borbonica".
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