Description: Thallus prostrate or prostrate with erect tufts to 7 cm, branching complanate showing distinct main axis with fine alternate branching, terete and polysiphonous with of 7 - 8 pericentral cells, ecorticate.

Habitat: Common. Epilithic or epiphytic in low water rock pools to 33 m sublittoral.

Distribution: Generally distributed around the British Isles especially in the sublittoral. Europe: Mediterranean, Azores, Portugal, Spain, France, Baltic Sea, Norway, Faroes and Iceland. Further afield: Morocco.

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

iNaturalist: Pterosiphonia parasitica at iNaturalist World Species Observations database.

WoRMS: Pterosiphonia parasitica at World Register of Marine Species. Accepted name: Deltalsia parasitica (Hudson) Díaz-Tapia & Rodríguez-Buján, 2022. AphiaID: 1649768.

Classification: Biota; Plantae; Biliphyta; Rhodophyta; Eurhodophytina; Florideophyceae; Rhodymeniophycidae; Ceramiales; Rhodomelaceae; Pterosiphonieae; Pterosiphonia