Description: Very small uniseriate filaments with prostrate and erect axes to 2 mm high. Many branches arising secund one from each cell of the erect axis.

Habitat: Common. Epiphytic on other algae, Zostera or epizoic on hydroids in the low littoral and sublittoral to 5 m.

Distribution: Generally distributed around the British Isles from the Shetlands to the Channel Islands. Europe: Mediterranean, Portugal, Atlantic coasts of Spain and France, Netherlands, Baltic Sea, Norway, Faeroes and Iceland. Greenland. Atlantic coast of North America: Canada, Maine, New Hampshire, Massachusetts, Rhode Island, Connecticut, New Jersey and Virginia. Further afield: Novaya Zemlya, Canary Islands, South Africa, Namibia, Mauretania and Korea.

Similar Species: All species of Acrochaetium are similar and microscopic examination is required for identification.

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

iNaturalist: Acrochaetium secundata at iNaturalist World Species Observations database.

WoRMS: Acrochaetium secundata at World Register of Marine Species.