Habitat: it lives in the infra and circalittoral zones, on sandy-slimy bottoms. Distribution: it can be found in a large part of the Mediterranean, but never common.
Notes: shell brittle, enough constant in outline, polygonal, higher than wider, valves globose, apex narrow and protuberant. Posterior margin strongly Insinuate, the first sinus of which is between umbo and auricle, the second one between auricle and submarginal fold, the third one is the posterior groove. Anteriorly it is angulated between the long margin of lunule and the beginning of ventral margin which is roundish, sometimes a little bit sinuous on ventral limb. Both auricle and sinuses are well broad and clear. Hinge with one small and obsolete cardinal tooth. Surface crossed by fine growth striae. Uniform dirty white in colour, muscle scars quite clear outside too. Juvenile specimens are more roundish in outline but they have already sinuosities in the posterior margin. A similar one, living however in deeper habitats, is T granulosa, recognizable besides the surface covered by a radial microsculpture, due to auricle missing in the posterior margin and due to one groove only, not much clear, making one real sinus in the posterior margin.
For a long time T biplicata was quoted in literature as T.flexuosa, Atlantic species, recognizable since it is bisinuated posteriorly, it has lunule margin shorter but more concave and auricle less elevated in the posterior margin. Thyasira polygona (Jeffreys, 1864), illustrated by Oliver & Killeen (2002), is considered as a synonym of T. biplicata by CLEMAM. The average measures are around 8-9 mm in height.