Species Account

Thyasira obsoleta (Verrill & Bush, 1898)

Thyasiroidea : Thyasiridae

Tebble name: n/a
Smith & Heppell name: Thyasira obsoleta (Verill & Bush, 1898)

To size: To 4mm. Shell Structure: Thin, fragile. Equivalve: Equivalve. Equilateral: Slightly to distinctly inequilateral, beaks behind the midline. Tumidity: Moderate. Outline: Obliquely ovate to pyriform (tear-drop shaped); anterior slightly to distinctly expanded; anterior dorsal margin sloping gently, weakly curved merging into broadly curved anterior; ventral margin evenly curved; posterior profile weakly to distinctly bi-angulate; posterior obliquely truncate, posterior dorsal angled by projecting auricle. Contour: Auricle low, rather long; submarginal sulcus depressed but edges weakly angled; lunule area a little flattened but no demarcating ridges.

Sculpture: Smooth with growth lines, often irregular. Margin: Smooth. Ligament: External, deeply sunken in auricle. Hinge: Hinge plate weak, slightly thickened below and anterior of beaks but lacking cardinal protuberance. Pallial Musculature: Muscle scars obscure. Periostracum: Not persistent. Colour: Shell white often with ferruginous deposits on posterior and anterior dorsal areas. Additional Characters: 2 demibranchs.

Distribution & Ecology

In British waters only known with certainty from north central North Sea in depths of 125-220m. Also known from Norwegian Faroes shelves.
Upper slope specimens from the Atlantic margin are considered to be a different species.
Payne & Allen, 1991 record it from bathyal and abyssal rise depths in the bay of Biscay but we have not confirmed this. Partial chemotrophic, suspension feeder (by inference from gill morphology), 2 demibranchs, however Dufour found no symbionts.
Gill anatomy – Dufour, 2005

Depth Range
Continental Shelf (to 200m)
Continental Margin Zone (200 - 500m)

Additional Information & Related Species

Additional Comments

This species has been extensively confused with Axinulus croulinensis making many records unreliable. We do not think it is conspecific with similar shells from the slope of the Atlantic Margin west of Shetland.

Related Species


Listed are literature citing Thyasira obsoleta (Verrill & Bush, 1898). 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.
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.
Verrill A E & Bush K J 1898. Revision of the deep water Mollusca of the Atlantic Coast of North America with descriptions of new genera and species Part 1 Bivalvia. Proceedings of the United States National Museum. 20: 775-901.


  • Conchological Society of Great Britain & Ireland
    Provides resources for understanding, identifying, recording, and conserving molluscs
    Check List of European Marine Mollusca
  • MarLIN
    The Marine Life Information Network for Britain and Ireland (MarLIN) provides information for marine environmental management, protection and education. It is a centre of excellence in spatially based and time-series marine biological information and supports good stewardship in the marine environment.
  • NBN Gateway
    National Biodiversity Network's Gateway. Use it to explore UK biodiversity data, as contributed by participating data providers.
  • BivAToL
  • MarBEF
  • Malacological Society
  • Unitas Malacologica
  • Census of Marine Life
  • MarBEF
    MarBEF, a network of excellence funded by the European Union and consisting of 94 European marine institutes, is a platform to integrate and disseminate knowledge and expertise on marine biodiversity, with links to researchers, industry, stakeholders and the general public.

Record last modified: 15/01/2014