Description: Thallus erect, cylindrical, usually hollow with constrictions at intervals and growing to a length of 30 cms.The crustose phase, Microspongium gelatinosum, considered to be the alternate phase of the life-cycle, is up to 0.5 mm thick and spreads to 30 mm or more in extent. It gives rise to simple filaments about 25 cells long.

Habitat: Both phases of S. lomentaria are common. Epilithic and epizoic in pools of the lower littoral and shallow sublittoral.

Distribution: Widespread around the British Isles. Europe: Mediterranean and the Black Sea, Azores, Portugal, Atlantic coasts of Spain and France, Belgium, Netherlands, Germany, Denmark, Baltic Sea, Sweden, Norway, Faroes, Jan Mayen, Bjornoya and Iceland. Atlantic coast of North America: Canada, Maine, New Hampshire, Massachusetts, Rhode Island, Connecticut and Long Island, New Jersey, Derlaware, Maryland, Virginia and Florida. Further afield: Arctic Seas: Murman Sea, Cumberland Sound on Baffin Island and the west coast of Greenland, Canary Islands, Caribbean, Pacific coast of North America from Alaska to California, Atlantic and Pacific South America, west and South Africa, Australia, New Zealand and Japan.

Similar Species: The crustose phase is very similar to other crustose phaeophytes, microscopic examination is required for determination. The erect Scytosiphon phase could be confused with Asperococcus fistulosus, however Asperococcus does not have regular constrictions.

Key Identification Features:

• Erect unbranched thalli with constrictions at intervals.

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

iNaturalist: Scytosiphon lomentaria at iNaturalist World Species Observations database.

WoRMS: Scytosiphon lomentaria at World Register of Marine Species. Accepted name: Scytosiphon lomentaria (Lyngbye) Link, 1833. AphiaID: 145869.

Classification: Biota; Chromista; Harosa; Heterokonta; Ochrophyta; Phaeophyceae; Fucophycidae; Ectocarpales; Scytosiphonaceae; Scytosiphoneae; Scytosiphon