''Solemya velum'', the Atlantic awning clam, is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

marine Marine is an adjective meaning of or pertaining to the sea or ocean. Marine or marines may refer to: Ocean * Maritime (disambiguation) * Marine art * Marine biology * Marine debris * Marine habitats * Marine life * Marine pollution Military * ...

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

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Solemyidae Solemyidae is a family of saltwater clams, marine protobranch bivalve mollusks in the order Solemyida. Biology Solemyids are remarkable in that their digestive tract is either extremely small or non-existent, and their feeding appendages are too ...

, the awning clams. This species is found along the eastern coast of North America, from

Nova Scotia Nova Scotia ( ; ; ) is one of the thirteen provinces and territories of Canada. It is one of the three Maritime provinces and one of the four Atlantic provinces. Nova Scotia is Latin for "New Scotland". Most of the population are native Eng ...

Florida Florida is a state located in the Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia, to the east by the Bahamas and Atlantic Ocean, and to ...

and inhabits subtidal sediments with high organic matter (OM) content and low Oxygen, such as salt ponds, salt marshes, and sewage outfalls. Species within the ''Solemya'' genus are distinguished by their reduced or absent guts and their association with symbiotic, chemosynthetic bacteria, which produce metabolic energy by oxidizing sulfide in order to fix carbon for their hosts. Other ''Solemya'' species have been discovered near hydrothermal vents and cold-seeps; environments where chemosynthesis and bacterial symbiosis are common.

Identification

''S. velum'' is characterized by having an elongated oval shell with parallel ventral and dorsal margins. Individuals range from 8 to 10 cm in length and the shells are lightly calcified, making them distinctively thin and brittle. The periostracum is a smooth, dark brown layer that extends past the shell edge. Unlike most bivalves, the interior of the hinge has no teeth. Sulfur-oxidizing bacterial symbionts are intracellular, harbored in the epithelial cells of ''S. velum'' gills and the tissue appears yellow when freshly collected due to the build-up of these sulfuric compounds. ''Solemya'' belongs to a group of "primitive" bivalves called protobranchs, which may be an ancestral or early diverging group. Most protobranchs live with the anterior end down in sediment so that the gills on the posterior end orient upwards. Opposite of other clams, water is circulated from the anterior end toward the posterior end and across the gills. The protobranchs usually have long extensions of the mouth called labial palps, which they extend into the sediment and pick up particles for feeding, though ''Solemya'' species lack labial palps because of their reliance on symbiotic bacteria. Some protobranchs, including ''Solemya'', also have a small flattened "sole" on their foot, which aids the clam in burrowing. The sole has left and right halves which can be folded together to collapse the foot into a narrow profile. The foot is then inserted into the sediment, the sole is unfolded to its wide configuration, and the foot is retracted to draw the clam down into the sediment. Because of their signature foot structure, ''Solemya'' creates distinctive U-shaped burrows and can completely bury itself with two thrusts of the foot in this manner. ''S. velum'' individuals have been found as deep as 100 m.

Ecology

Most bivalve species are filter feeders, though with their reduced guts and reliance on symbiotic bacteria, ''Solemya'' species either seldom filter-feed or abandoned filter-feeding altogether. Whether or not ''S. velum'' engages in filter feeding as a secondary food source is still an active area of research. The bacterial symbionts within ''S. velum'' and other ''Solemya'' species are chemoautotrophic, able to fix Carbon by using chemical energy from sulfur oxidation reactions and taking up . The presence of these clams and their symbionts in areas with high woody debris or sewage is critical in cycling carbon and breaking down sulfur compounds, reducing the toxicity of near-anoxic sediments.

Scientific interest

''S. velum'' is considered to be a model organism for studying bacterial symbiosis in bivalves. More accessible than its deep-sea relatives, ''S. velum'' can be collected from intertidal sediments and is easy to maintain in laboratory experiments. The genome of ''S. velum'' was sequenced in 2006 and is valuable for studying the relationships between animal and bacteria cells. The carbon-fixation capabilities of ''S. velum'' symbionts are an active area of research for the importance of consumption in marine carbon cycling.

References

{{Taxonbar, from=Q3014755 Solemyidae Bivalves of New Zealand Taxa named by Thomas Say Chemosynthetic symbiosis Bivalves described in 1822