Description: This bivalve has an almost circular shell, especially when young, although it can be more oval or pear-shaped in older animals. The shell is up to 11 cm long, rarely larger, but there can be considerable variation in shape and distortion of shells depending on the habitat in which they are growing. Usually off white or cream in colour with light brown banding on the upper valve. The lower (left) valve is convex while the upper (right) valve is flat. Shell surface is rough, and the shell margin has numerous small undulations (not markedly wavy like Magallana gigas). Can be quite inconspicuous as it blends in well in surrounding habitat and can be attached (lower half) to rock or seabed.

Habitat: Mud, sand, gravel on the lower shore to up to 80 m depth. Also found in estuaries.

Distribution: Found all around Britain and Ireland where there is suitable habitat. While it occurs naturally it has also been introduced in some areas. It’s much less abundant than in the past mainly due to overfishing, and is currently under competitive pressure from non-native species such as the slipper limpet Crepidula fornicata and the Pacific oyster Magallana gigas.

Similar Species: Could potentially be confused with the Pacific oyster Magallana gigas however Ostrea edulis is more circular in shape and does not bear the dark purple markings of M. gigas, nor does it have a markedly wavy shell margin.

Key Identification Features:

• Almost circular bivalve.
• Numerous small undulations at shell margin.
• Rough shell surface.
• Lower valve convex and upper valve flat.

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

iNaturalist: Ostrea edulis at iNaturalist World Species Observations database.

GBIF data for Ostrea edulis

WoRMS: Ostrea edulis at World Register of Marine Species. Accepted name: Ostrea edulis Linnaeus, 1758. AphiaID: 140658.

Classification: Biota; Animalia; Mollusca; Bivalvia; Autobranchia; Pteriomorphia; Ostreida; Ostreoidea; Ostreidae; Ostreinae; Ostrea