Temporal range: Paleocene?/Eocene–recent
|A live individual of an unidentified species of Juliidae|
|A drawing of the shell (the exterior of the right valve) of a taxon named "Julia borbonica"|
E. A. Smith, 1885
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 (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, a related but very different class of mollusks.
In the past 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.
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.
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
Up until the mid 20th century, these creatures were still considered to be bivalves. Then finally in 1959, living individuals of one species were collected on the green alga, Caulerpa, in Japan. It was immediately clearly visible that these animals are 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).
Once the habitat, appearance, and life habits of these very small and inconspicuous animals were understood, in subsequent years researchers were able to find a number of other species and other genera in different parts of the world, also living on various species of Caulerpa.
This family is within the clade Sacoglossa (according to the taxonomy of the Gastropoda by Bouchet & Rocroi, 2005).
The family Juliidae consists of the following subfamilies (according to the taxonomy of the Gastropoda by Bouchet & Rocroi, 2005):
- subfamily Juliinae E. A. Smith, 1885 - synonym: Prasinidae Stoliczka, 1871
- subfamily Bertheliniinae Keen & A. G. Smith, 1961 - synonym: Tamanovalvidae Kawaguti & Baba, 1959
- † (fossil) subfamily Gougerotiinae Le Renard, 1980
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.
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.
While Jensen (2007) recognized two recent genera with a few subgenera in the genus Berthelinia. Recent species listed here are based on Jensen (2007), fossil genera and species are based on Le Renard (1996):
- Julia Gould, 1862 - synonym: Prasina Deshayes, 1863
- (fossil) Candinia Le Renard J., Sabelli B. & Taviani M. 1996
- Berthelinia Crosse, 1875 - type genus of the subfamily Bertheliniinae
- subgenus Berthelinia Crosse, 1875
- (recent) Berthelinia caribbea Edmunds, 1963
- (recent) Berthelinia chloris (Dall, 1918)
- (invalid recent species) Berthelinia corallensis Hedley, 1920
- (recent) Berthelinia darwini Jensen, 1997
- (recent) Berthelinia ganapati Sarma, 1975
- (recent) Berthelinia pseudochloris Kay, 1964
- (recent) Berthelinia rottnesti Jensen, 1993
- (recent) Berthelinia schlumbergeri Dautzenberg, 1895
- (recent) Berthelinia waltairensis Sarma, 1975
- (fossil) Berthelinia elegans Crosse, 1875
- subgenus Midorigai : synonym of Berthelinia Crosse, 1875
- subgenus Tamanovalva Kawaguti & Baba, 1959 : synonym of Berthelinia Crosse, 1875
- subgenus Edenttellina : synonym of Berthelinia Crosse, 1875
- subgenus Berthelinia Crosse, 1875
- (fossil?) Anomalomya Cossmann, 1887
- (fossil?) Namnetia Cossmann, 1906
- (fossil?) Squamulinia Le Renard, 1989
- (fossil) Gougerotia Le Renard, 1980 - type genus of the subfamily Gougerotiinae
- (fossil) Gougerotia orthodonta Le Renard, 1980
This article incorporates public domain text from reference.
- Smith E. A. (1885). "Report on the scientific results of the voyage of H. M. S. Challenger". Zoology 13(1): 269.
- Le Renard J., Sabelli B. & Taviani M. (March 1996). "On Candinia (Sacoglossa: Juliidae), a New Fossil Genus of Bivalved Gastropods". Journal of Paleontology 70(2): 230-235. JSTOR 1306386
- George Washington Tryon, Jr. (1884). Structural and systematic conchology: an introduction to the study of the Mollusca. Volume III. Philadelphia, published by the author, page 267.
- 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 University 5(3-4): 177-184.
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- Rudman W. B. (16 October 2001). "Midorigai australis Burn, 1960". Sea Slug Forum. Australian Museum, Sydney, accessed 10 May 2009.
- Burn R. F. (1965). "Rediscovery and taxonomy of Edenttellina typica Gatliff and Gabriel". Nature 206(4985): 735-736.
- Burn R. (1966). "The Opisthobranchs of a caulerpan microfauna from Fiji". Proceedings of the Malacological Societ London 37: 45. abstract
- Rudman W. B. (11 March 2002). "Tamanovalva limax Kawaguti & Baba, 1959". Sea Slug Forum. Australian Museum, Sydney, accessed 10 May 2009.
- Gatliff J. H. & Gabriel C. J. (1911). "On some new species of Victorian marine mollusca". Proceedings of the Royal Society of Victoria 24: 189-192.
- Rudman W. B. (16 October 2001). "Edenttellina typica Gatliff & Gabriel, 1911". Sea Slug Forum. Australian Museum, Sydney, accessed 10 May 2009.
|Wikimedia Commons has media related to Juliidae.|
- Cory Pittman & Pauline Fiene. 2009. Juliidae. Sea Slugs of Hawaii.
- Images of 4 species of Juliidae in Japan
- Photos of Julia exquisita at Sea Slug Forum
- Detailed photos of the shell of Julia exquisita at Sea Slug Forum
- (Japanese) http://taxonomist.symphonic-net.com/contents/Others/Julia/julia!.html