Species description: Elongate oval-shaped bivalve, reaching up to 180 mm in length. The shell is thick and rough, and the shell margin is markedly wavy – giving it a ‘sawtooth’ appearance, especially in older specimens. It is usually off-white or grey in colour and bears dark purple banding or patches. The lower valve (shell) is usually cemented to a hard substratum, but they can also grow almost completely upright in crowded areas.

Habitat: Lower shore to around 80 m depth on a range of substrata from rocky shores to artificial structures such as those in harbours and marinas. Commercially farmed in many locations.

Distribution: Invasive non-native species that is now widely established in the wild around Britain and Ireland. Aquaculture of this species is still ongoing on a large scale despite its spread.

Similar Species: Could be confused with the native oyster Ostrea edulis, however Magallana gigas is oval and elongate rather than almost circular, and has a markedly wavy shell margin (O. edulis only has small undulations). M. gigas also frequently has dark purple banding which is absent in O. edulis.

Key Identification Features:

• Elongate, oval-shaped shell.
• Thick and rough shell surface with a markedly wavy shell margin.
• Often has dark purple patches or banding.

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

iNaturalist: Magallana gigas at iNaturalist World Species Observations database.

WoRMS: Magallana gigas at World Register of Marine Species. Accepted name: Magallana gigas (Thunberg, 1793). AphiaID: 836033.

Classification: Biota; Animalia; Mollusca; Bivalvia; Autobranchia; Pteriomorphia; Ostreida; Ostreoidea; Ostreidae; Crassostreinae; Magallana