Description: A heavy, solid shell with a nearly circular outline, up to 6.5 cm in length. Valves are unequal, the right valve is slightly more convex, with concentric ridges which have fine lines between them. It is dirty white to light brown in colour, with a pale orange or pink tint to the umbones. Radiating rays of orange, red or brown may be visible. The outer surface of the shell sometimes partially covered in a yellow-brown periostracum. Growth stages often clearly visible. Teeth are relatively well developed in this species and situated on a prominent hinge plate. Each valve has 2 cardinal, 1 posterior and 1 lateral. The right valve has a bifid posterior tooth while the anterior is bifid on the left. Shell interior usually orange with a white margin around the outer edge. Pallial sinus is deep and tongue-shaped, and may be deeply coloured.

Habitat: Muddy sand, coarse sand or shelly gravel. Found from just offshore to around 150 m, and very occasionally found intertidally.

Distribution: Recorded from all around Britain, but records from Ireland seem limited.

Similar Species: Could be confused with some other superficially similar bivalves. Careful inspection of diagnostic features such as cardinal and lateral teeth, pallial sinus and overall shape and appearance of the shell should help to distinguish.

Key Identification Features:

• Heavy, solid shell with unequal valves.
• Dirty white to light brown with pale orange or pink tint to umbones.
• Radiating rays of red, orange or brown possibly visible.
• Orange interior with white margin.
• Deep, tongue-shaped pallial sinus.

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

iNaturalist: Arcopagia crassa at iNaturalist World Species Observations database.

GBIF data for Arcopagia crassa

WoRMS: Arcopagia crassa at World Register of Marine Species. Accepted name: Arcopagia crassa (Pennant, 1777). AphiaID: 141577.

Classification: Biota; Animalia; Mollusca; Bivalvia; Autobranchia; Heteroconchia; Euheterodonta; Imparidentia; Cardiida; Tellinoidea; Tellinidae; Arcopagiinae; Arcopagia