Parathyasira granulosa (Monterosato, 1874)
Thyasiroidea : Thyasiridae
To size: To 10mm. Shell Structure: Thin, fragile. Equivalve: Equivalve. Equilateral: Equilateral. Tumidity: Moderate. Outline: Ovate-rhomboidal, higher than long; anterior dorsal (lunule) margin short, excavated; anterior roundly angulate to obliquely truncate; ventral margin narrowly rounded to almost straight when angulate with posterior; posterior margin subtruncate to slightly indented; posterior dorsal slope long. Contour: Auricle absent, submarginal sulcus long, distinct; posterior area flattened, posterior angle very weak.
Sculpture: Minutely granular, granules dense arranged radially but this pattern is not obvious; when worn surface with growth lines and irregular dents only. Margin: Smooth. Ligament: External, sunken but visible extending half length of submarginal sulcus. Hinge: Hinge plate weak, single cardinal protuberance in RV, corresponding depression in LV. Pallial Musculature: Muscle scars obscure. Periostracum: Thin, not apparent. Colour: Shell white, often with a thin, brown or rust coloured deposit. Additional Characters: 2 demibranchs.
Distribution & Ecology
Also known from the Mediterranean and Gulf of Cadiz, absence of records from British and Irish shelf edge unexplained. Partial chemotrophic, suspension feeder (by inference from gill morphology), 2 demibranchs, however Dufour found no symbionts.
Gill anatomy – Dufour, 2005.
Continental Shelf (to 200m)
Continental Margin Zone (200 - 500m)
Additional Information & Related Species
T. subcircularis has a more rounded subcircular outline, the granules create a very obvious arrangement of radial raised striations, a bathyal species 800-2150m.
Thyasiroidea : Thyasiridae
Listed are literature citing Parathyasira granulosa (Monterosato, 1874). Reference containing the species Type Description is highlighted.
Dufour S C 2005. Gill anatomy and the evolution of symbiosis in the bivalve family Thyasiridae. Biological Bulletin. 208: 200-212.
Monterosato T A 1874. Recherches conchyliologiques, effectuées au Cap Santo Vito, en Sicile. (Traduz. dall'italiano di H. Crosse). Journal de Conchyliologie. 22 (3): 243-282.
Olabarria C. 2005. Patterns of bathymetric zonation of bivalves in the Porcupine Sea Bight and adjacent abyssal plain, NE Atlantic. Deep-Sea Research I. 52: 15-31.
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.
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