Species Account

Thyasira (Thyasira) flexuosa (Montagu, 1803)

Thyasiroidea : Thyasiridae

Tebble name: Thyasira flexuosa (Montagu)
Smith & Heppell name: Thyasira flexuosa (Montagu, 1803)

To size: To 12mm. Shell Structure: Thin, fragile. Equivalve: Equivalve. Equilateral: Equilateral. Tumidity: Moderate. Outline: Ovate, higher than long; anterior dorsal margin excavated some with a short subtruncate section at junction with narrowly rounded anterior; ventral margin curved; posterior profile distinctly biangulate; posterior margin sulcate posterior dorsal margin weakly sulcate depending on expression of auricle. Contour: Umbo projecting; auricle projecting but strongly to weakly defined about 2/3 length of strongly demarcated submarginal sulcus. First posterior fold prominent and subacute, posterior sulcus well developed; second posterior fold strong and subacute. Larval shell160-180microns.

Sculpture: Of growth lines and stops often with irregular dents and weak ridges. Margin: Smooth. Ligament: Deeply sunken within auricle about 1/2 its length. Hinge: Weak, a small cardinal peg in RV, LV with a corresponding depression. Pallial Musculature: Muscle scars obscure. Periostracum: Thin not persistent. Colour: Shell white, often with anterior dorsal and posterior ferruginous coatings. Additional Characters: 2 demibranchs.

Distribution & Ecology

Widely distributed from the intertidal and shelf to over 150m. Chemosymbiotic, bacterial dependence high but can suspension feed. In mud, muddy sand from the intertidal and shelf.
Gross anatomy – Allen, 1958
Symbiosis – Southward, 1986; Dando & Southward, 1986
Gill anatomy – Dufour, 2005

Depth Range
Continental Shelf (to 200m)

Additional Information & Related Species


Listed are literature citing Thyasira (Thyasira) flexuosa (Montagu, 1803). Reference containing the species Type Description is highlighted.

Allen J A 1958. On the basic form and adaptation to habitat in the Lucinacea (Eulamellibranchia). Philosophical Transactions of the Royal Society of London Series B. 241: 421-484.
Dando P R & Southward A J 1986. Chemoautotrophy in the bivalve molluscs of the genus Thyasira. Journal of the Marine Biological Association of the United Kingdom. 66: 915-929.
Dufour S C 2005. Gill anatomy and the evolution of symbiosis in the bivalve family Thyasiridae. Biological Bulletin. 208: 200-212.
Montagu G 1803. Testacea Britannica, or natural history of British shells, marine, land and the fresh-water, including the most minute: systematically arranged and embellished with figures Romsey, London. 606pp, 16pls.
Oliver P G & Killeen I J 2002. The Thyasiridae (Mollusca: bivalvia) of the British continental shelf and North Sea Oilfields. Studies in Marine Biodiversity and Systematics from the National Museum of Wales. BIOMOR Reports. 3: 1-73.
Payne C.M. & Allen J.A. 1991. The morphology of deep-sea Thyasiridae (Mollusca: Bivalvia) from the Atlantic Ocean. Philosophical Transactions of the Royal Society of London Series B. 334: 481-566.
Southward E C 1986. Gill symbionts in thyasirids and other bivalve molluscs. Journal of the Marine Biological Association of the United Kingdom. 66: 889-914.
Taylor J D, Williams S T & Glover E A 2007. Evolutionary relationships of the bivalve family Thyasiridae (Mollusca: Bivalvia), monophyly and superfamily status. Journal of the Marine Biological Association of the United Kingdom. 87: 565-574.


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Record last modified: 17/05/2016