Description: Thallus to 2 m long, compressed tough and leatherly, attached by strong holdfast. Branches distichous and regularly alternate. Air bladders, up to 5 cms long, are oblong and stalked towards the ends of the branches. The air bladders are divided by cross walls visible when sectioned longitudinally.

Habitat: Common. Low littoral rock pools and upper sub-littoral.

Distribution: Widespread around the British Isles. Europe: Portugal, Atlantic coasts of Spain and France, Netherlands, Baltic Sea, Norway and the Faroes.

Key Identification Features:

• The stalked linear air bladders and zig-zag main axis are characteristic.

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

iNaturalist: Halidrys siliquosa at iNaturalist World Species Observations database.

WoRMS: Halidrys siliquosa at World Register of Marine Species.