Description: Thallus small to 10 cms long of fine unbranched filaments of two rows of cells (biseriate).

Habitat: Inconspicuous. Growing as tangled masses on mud in the littoral or brackish water.

Distribution: Widespread athroughout the British Isles. Europe: Spain, France, Netherlands, Baltic Sea, Norway, Sweden, Faroes, Spitzbergen and Iceland. Greenland. Atlantic coast of North America: Canada, Maine, New Hampshire, Massachusetts, Rhode Island, Connecticut, New Jersey, Delaware, Maryland and Virginia. Further afield: Canary Islands, Pacific coast of North America from Alaska to California, Japan and South Africa.

Key Identification Features:

• Biseriate filament.

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

iNaturalist: Percursaria percursa at iNaturalist World Species Observations database.

WoRMS: Percursaria percursa at World Register of Marine Species.