Description: A thin and fragile, almost circular shell with a slightly irregular outline that reaches a maximum size of 4 cm. White to light yellow with a transparent satiny periostracum. Structure of concentric grooves with clear growth stages visible on outer surface of valves, and a smooth shell margin. 3 cardinal teeth in left valve of which the central is bifid, 2 in right of which posterior is bifid. Very large pallial sinus.

Habitat: Muddy sand, gravel or muddy gravel, including muddy shelly gravel, from shallow sublittoral to around 60 m.

Distribution: Found all around Britain and Ireland.

Similar Species: Could be confused with Dosinia lupinus or Dosinia exoleta which have much thicker, more solid shells.

Key Identification Features:

• Thin, fragile shell.
• 3 cardinal teeth in left valve, central is bifid.
• 2 in right valve, posterior is bifid.
• Very large pallial sinus.

Distribution Map from NBN: Mysia undata at National Biodiversity Network mapping facility, data for UK.

iNaturalist: Mysia undata at iNaturalist World Species Observations database.

WoRMS: Mysia undata at World Register of Marine Species.