These are sacoglossan (sap-sucking) 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. Juliidae are known from the Eocene period to the Recent, but they probably first appeared during the Paleocene.[3]
Taxonomy as "bivalves"
These bivalved gastropods were for a long time only known from fossils and dead material. Because of this, they had been described as being somewhat atypical bivalves. In the late 19th century they were classified among the bivalves, within the family Mytilidae, the mussels.[4]
The similarity of the shells of Juliidae to those of bivalves does not mean that these snails are closely related to bivalves; this is an example of convergent evolution.
Discovery of live animals
Until the mid-20th century, these creatures were still considered to be bivalves. Then, in 1959, living individuals of one species were collected on the green alga, Caulerpa, in Japan. It was immediately clear that these animals were, in fact, unusual gastropods with a two-part shell. The first-discovered live species of bivalved gastropod was Tamanovalva limax, described by Kawaguti & Baba (1959).[5]
Once the habitat, appearance, and life habits of these very small and inconspicuous animals were understood, researchers in subsequent years were able to find a number of other species and genera in different parts of the world, also living on various species of Caulerpa.
Drawing of the interior of the left valve of the shell of "Julia borbonica".Drawing of the interior of the right valve of the shell of "Julia borbonica".
As Tryon (1884)[4] 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.[8] The two valves are usually thin and translucent.
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 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.[10]
After hatching, the juvenile snails immediately take their place on algae (the larval phase of veliger is extremely short).[11]
Feeding habits
Juliidae feed on green algae[8] of the genus Caulerpa. Some species of Juliidae feed only on one species of Caulerpa; others feed on multiple species of this green alga.
Based on a classification by Jensen (1996),[12] three recent genera were recognized in the family Juliidae:[13]Julia Gould, 1862; Berthelinia Crosse, 1875; Tamanovalva Kawaguti & Baba, 1959.
While Jensen (2007)[14] recognized two recent genera with a few subgenera in the genus Berthelinia. Recent species listed here are based on Jensen (2007),[14] fossil genera and species are based on Le Renard (1996):[3]
Juliinae
Julia Gould, 1862 - synonym: Prasina Deshayes, 1863
Sacoglossa, commonly known as the sacoglossans or the "solar-powered sea slugs", are a superorder of small sea slugs and sea snails, marine gastropod mollusks that belong to the clade Heterobranchia. Sacoglossans live by ingesting the cellular contents of algae, hence they are sometimes called "sap-sucking sea slugs".
Stiliger is a genus of small and minute sacoglossan or sap-sucking sea slugs. They are marine gastropod mollusks in the family Limapontiidae.
A valve is each articulating part of the shell of a mollusc or another multi-shelled animal such as brachiopods and some crustaceans. Each part is known as a valve or in the case of chitons, a "plate". Members of two classes of molluscs, the Bivalvia (clams) and the Polyplacophora (chitons), have valves.
Chelidonura is a genus of small, sometimes colorful, sea slugs. These are headshield slugs or cephalaspideans, marine opisthobranch gastropod mollusks in the family Aglajidae.
Mexichromis is a genus of colourful sea slugs, dorid nudibranchs, shell-less marine gastropod mollusks in the family Chromodorididae. Current synonymy follows a revision of Chromodorididae which used molecular phylogeny.
Julia is a genus of minute sea snails, marine gastropod mollusks or micromollusks in the superfamily Oxynooidea.
Berthelinia is a genus of gastropod belonging to the family Juliidae.
Julia exquisita is a small species of sea snail with a green bivalve shell. It is a marine gastropod mollusk in the family Juliidae.
Julia japonica is a species of a sea snail with a shell comprising two separate hinged pieces or valves. It is a marine gastropod mollusk in the family Juliidae.
Julia mishimaensis is a species of a sea snail with a shell comprising two separate hinged pieces or valves. It is a marine gastropod mollusk in the family Juliidae.
Julia zebra is a species of a sea snail with a shell comprising two separate hinged pieces or valves. It is a marine gastropod mollusk in the family Juliidae.
Berthelinia caribbea is a species of a sea snail with a shell comprising two separate hinged pieces or valves. It is a marine gastropod mollusc in the family Juliidae.
Berthelinia waltairensis is a species of a sea snail with a shell comprising two separate hinged pieces or valves. It is a marine gastropod mollusc in the family Juliidae.
Berthelinia limax is a species of a sea snail with a shell comprising two separate hinged pieces or valves. It is a marine gastropod mollusc in the family Juliidae.
Berthelinia typica is a species of sea snail with a shell comprising two separate hinged pieces or valves. It is a marine gastropod mollusc in the family Juliidae. It was first described as Edentellina typica in 1911 by Gatliff and Gabriel.
Hermaea oliviae is a species of sacoglossan sea slug, a shell-less marine opisthobranch gastropod mollusk in the family Hermaeidae.
Hermaea zosterae is a species of sacoglossan sea slug, a shell-less marine opisthobranch gastropod mollusk in the family Hermaeidae.
Aplysiopsis brattstroemi is a species of sacoglossan sea slug, a shell-less marine opisthobranch gastropod mollusk in the family Hermaeidae.
Aplysiopsis elegans is a species of sacoglossan sea slug, a shell-less marine opisthobranch gastropod mollusk in the family Hermaeidae.
References
This article incorporates public domain text from reference.[4]
1 2 3 4 Le Renard J., Sabelli B. & Taviani M. (March 1996). "On Candinia (Sacoglossa: Juliidae), a New Fossil Genus of Bivalved Gastropods". Journal of Paleontology70(2): 230-235. JSTOR1306386
1 2 Kawaguti S. & Baba K. (1959). "A preliminary note on a two-valved sacoglossan gastropod, Tamanovalva limax, n. gen., n. sp., from Tamano, Japan". Biological Journal Okayama University5(3-4): 177-184.
↑ Keen & Smith A. G. (1961). Proceedings of the California Academy of Sciences, ser. 4, 30(2): 50.
↑ Le Renard J. (1980). Bulletin d'Information des Géologues du Bassin de Paris17(2): 23.
1 2 3 (in Czech) de Bruyne R. H. (2004). Encyklopedie ulit a lastur. Rebo Productions, 336 pp., ISBN80-7234-288-6, page 223.
1 2 3 Jensen K. R. (1996). "Phylogenetic systematics and classification of the Sacoglossa (Mollusca, Gastropoda, Opisthobranchia)". Philosophical Transactions of the Royal Society London B Biological Sciences351(1335): 91-122. doi:10.1098/rstb.1996.0006.
↑ Kay E. A. (1964). "A new species of Berthelinia and its associated sacoglossans in the Hawaiian Islands". Proceedings of the Malacological Society of London36: 191-197. abstract.
↑ Pittman C. & Fiene P. (2009). "Berthelinia pseudochloris". Sea Slugs of Hawaii, last change of the page 27 January 2009, accessed 10 May 2009.
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