''Ctena orbiculata'', commonly known as the dwarf tiger lucine, is a species of

bivalve Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bival ...

mollusc Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is esti ...

in the

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Lucinidae Lucinidae, common name hatchet shells, is a family of saltwater clams, marine bivalve molluscs. These bivalves are remarkable for their endosymbiosis with sulphide-oxidizing bacteria. Characteristics The members of this family have a worldwide ...

. It can be found along the Atlantic coast of North America, ranging from

North Carolina North Carolina () is a state in the Southeastern region of the United States. The state is the 28th largest and 9th-most populous of the United States. It is bordered by Virginia to the north, the Atlantic Ocean to the east, Georgia and So ...

to the

West Indies The West Indies is a subregion of North America, surrounded by the North Atlantic Ocean and the Caribbean Sea that includes 13 independent island countries and 18 dependencies and other territories in three major archipelagos: the Greater A ...

Description

''Ctena orbiculata'' grows to maximum length of . The shell valves are nearly circular, the outer surface being sculptured with fine concentric rings and rather coarser radial lines. The lunule is elongate. The valves can be white, pale yellow or pale orange, but the interior is never pinkish. The shell is more inflated than that of the rather larger tiger lucine (''

Codakia orbicularis ''Codakia orbicularis'' , or the tiger lucine, is a species of bivalve mollusc in the family Lucinidae. It can be found along the Atlantic coast of North America, ranging from Florida to the West Indies. Description ''Codakia orbicularis'' grows ...

''). Like other members of its family

, ''Ctena orbiculata'' does not have an inhalant siphon, instead rolling its elongated foot into a mucus-lined tube and drawing water into the gill cavity through this. It does have an exhalant siphon which is formed from a highly extensible mantle flap and can be inverted and drawn back into the shell.

Distribution and habitat

''Ctena orbiculata'' is native to the western Atlantic Ocean where its range extends from

to the

Caribbean Sea The Caribbean Sea ( es, Mar Caribe; french: Mer des Caraïbes; ht, Lanmè Karayib; jam, Kiaribiyan Sii; nl, Caraïbische Zee; pap, Laman Karibe) is a sea of the Atlantic Ocean in the tropics of the Western Hemisphere. It is bounded by Mexico ...

. It lives immersed in soft sediment on the seabed. Its maximum depth is .

Ecology

''Ctena orbiculata'' is present in large quantities in the sediments associated with turtlegrass, ''

Thalassia testudinum ''Thalassia testudinum'', commonly known as turtlegrass, is a species of marine seagrass. It forms meadows in shallow sandy or muddy locations in the Caribbean Sea and the Gulf of Mexico. Turtle grass and other seagrasses form meadows A meado ...

'', in Bermuda. The gills of the mollusc contain

symbiotic Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasit ...

bacteria able to oxidise sulphur. These chemoautotrophic bacteria use the energy released by the oxidation of sulphur compounds to fix carbon dioxide and convert the products into more complex organic molecules which become available to the mollusc. Oxygen-containing water is drawn into the mollusc's gills where the sulphide present in the sediment can be oxidised to non-toxic thiosulphate. The bacteria use oxygen or the nitrate present in the water as an electron acceptor, and oxidise thiosulphate further. This symbiotic arrangement may have allowed bivalves such as ''Ctena orbiculata'' to colonise sediments not suited to other organisms. During periods of starvation in the laboratory, ''Ctena orbiculata'' soon consumes the bacterial symbionts in its gill chambers. On release into ''

'' seagrass beds, the molluscs quickly reacquires the bacteria from the environment.

References

{{Taxonbar, from=Q13503260 Lucinidae Molluscs of the Atlantic Ocean Bivalves described in 1808 Taxa named by George Montagu (naturalist)