Shells equivalve, often inflated, with pallial margin smooth; ligament sunken when external; posterior area often with a submarginal sulcus, otherwise flattened; sculpture mainly made up of irregular commarginal growth marks. « The Thyasiridae is one of the seven bivalve families that are chemosymbiotic and associated with sites of organic enrichment, methane seeps and to a lesser degree hot vents. Unlike most other chemosymbiotic bivalve families the symbiosis is not obligate, some species devoid of symbionts while others are heavily or totally dependent on them (Southward, 1986; Dufour, 2005) » (Graham & Rodrigues, 2017).
 

« Shell subovate; lunule and escutcheon shallow to deep; sculpture of commarginal striae, with shallow posterior radial sulcus; hinge edentulous. » – Coan & Valentich-Scott: Bivalve seashells of tropical West America vol.I, Santa Barbara 2012, p.367. – But there is, in fact, one cardinal tooth.
 

Shell slightly inequilateral, subovate to subcircular, anteriorly rounded, posteriorly subacute; posterior fold obsolete; umbones prominent, prosogyrate; sculpture made up of weak commarginal growth striae, with some growth stops. Hinge weak.
 

« The shells are small to minute, ovate to obliquely ovate in outline with a sulcate or truncated posterior area and usually a sinuate posterior margin. The hinge is weak with or without a single cardinal tubercle or flange. » – Oliver & Killeen: “The Thyasiridae (Mollusca: Bivalvia) of the British Continental Shelf and North Sea Oil Fields”, Studies in marine biodiversity and systematics from the National Museum of Wales vol.III, Cardiff 2002, p.62.