Species description: A brown seaweed that is usually 3-7 cm across but can grow up 25 cm. It is olive-brown to yellow-brown in colour. It forms a thin-walled, hollow sphere with older specimens becoming furrowed, and it tears very easily (like paper). Named the "oyster thief" as specimens attached to oysters shells can float away with the oyster still attached. Attaches by root-like filaments from a single point at the base.

Habitat: Not uncommon. Epiphytic in lower littoral rock pools and sublittoral to 3 m depth.

Distribution: Widespread on the coasts of Britain and Ireland, but more common in the southern and western shores. Europe: Mediterranean, Portugal, Atlantic coasts of Spain and France, Belguim, Netherlands, Denmark, Baltic and Norway. Atlantic coast of North America: Canada. Further afield: Pacific coast of North America from Alaska to California, the Canary Islands, West Africa, Australia and New Zealand.

Similar Species: Leathesia difformis is also hollow, solid when young, gelatinous, but is never membranous and does not tear like paper. Colpomneia sinuosa is not found in the British Isles.

Key Identification Features:

• Spherical, hollow and membranous.
• Easily torn.

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

iNaturalist: Colpomenia peregrina at iNaturalist World Species Observations database.

WoRMS: Colpomenia peregrina at World Register of Marine Species. Accepted name: Colpomenia peregrina Sauvageau, 1927. AphiaID: 145856.

Classification: Biota; Chromista; Harosa; Heterokonta; Ochrophyta; Phaeophyceae; Fucophycidae; Ectocarpales; Scytosiphonaceae; Hydroclathreae; Colpomenia