Description: Uniseriate filaments to 20 cms long, stiff straight and unbranched. Cells large, barrel-shaped with constrictions at the septae. Visible to the naked eye.

Habitat: Not uncommon and not abundant, in littoral rock pools.

Distribution: Widespread throughout the British Isles from the Shetlands to the Channel Islands, though poorly recorded in some areas. Europe: Spain, France, Baltic Sea, Norway, Faroes and Iceland. Atlantic coast of North America: Canada, Maine, New Hampshire and New Jersey. Further afield: Arctic Seas from Spitzbergen, the Murman Sea, the Kara Sea, American Arctic sea, Baffin Island and west coast of Greenland.

Key Identification Features:

• Filaments clearly beaded.

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

iNaturalist: Chaetomorpha melagonium at iNaturalist World Species Observations database.

WoRMS: Chaetomorpha melagonium at World Register of Marine Species.