page_title: Valve (mollusc)
section_title: Bivalved gastropods
hierarchical_section_title: Valve (mollusc) / Bivalved gastropods
caption_attribution_description: English: photo of an unidentified species of Juliidae.
context_page_description: A mollusc valve is each articulating part of the shell of a mollusc. Each part is known as a valve or in the case of chitons, a "plate". Members of two classes of molluscs: the Bivalvia and the Polyplacophora have valves.
  Species within one family of very unusual small sea snails, marine opisthobranch gastropods in the family Juliidae, also have two articulating shells or valves, which resemble those of a bivalve. This exceptional family is commonly known as the bivalved gastropods. Gastropods in general are sometimes called "univalves", because in those that have a shell, the shell is usually in one part.
context_section_description: The great majority of shelled gastropods or snails have a shell in one part, hence the older name "univalve". The gastropod operculum, when present, even when it is composed mostly of calcium carbonate, is not considered to be a valve.
  In contrast, species within one family of small sea snails, the Juliidae, opisthobranch gastropod molluscs, have a hinged shell which is composed of two parts joined by a ligament. These two parts very closely resemble the two valves of a bivalve. This group of species are often referred to as "bivalved gastropods".  These are sacoglossans in several genera including Julia, Berthelinia, Midorigai, Edenttellina, Tamanovalva, and Candinida.
  These bivalve gastropods were for a long time known only from fossils and dead material. Because of this, they had been described as being somewhat atypical bivalves. It was not until living individuals were found in the late 20th century that it was understood that these are in fact very unusual gastropods.
caption: A live individual of an unidentified species of bivalved gastropod in the family Juliidae
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