Description: Thallus of densely branched filaments up to 15 cms long. Branches of several types including hooked and spinous also descending rhizoids these bind the filaments into "ropes".

Habitat: Generally common. Mid and low littoral rock pools.

Distribution: Widespread around the British Isles. Europe: Spain, France, Netherlands, Helgoland, Baltic Sea, Norway, Faroes, Spitzbergen, Finland and Iceland. Atlantic coast of North America: Canada, Maine, New Hampshire, Massachusetts, Rhode Island, Connecticut and New Jersey. Further afield: Arctic Seas - Murman Sea, the White Sea, the Kara Sea to Baffin Island and the West coast of Greenland, Pacific coast of North America from Bearing Sea to Oregon, Chile.

Similar Species: Spongomorpha aeruginosa never has spinous branches.

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

iNaturalist: Spongomorpha arcta at iNaturalist World Species Observations database.

WoRMS: Spongomorpha arcta at World Register of Marine Species. Accepted name: Acrosiphonia arcta (Dillwyn) Gain, 1912. AphiaID: 144407.

Classification: Biota; Plantae; Viridiplantae; Chlorophyta; Chlorophytina; Chlorophyceae; Acrosiphoniales; Acrosiphoniaceae; Spongomorpha