A sea fir (Eudendrium arbuscula)

Distribution data supplied by the Ocean Biodiversity Information System (OBIS). To interrogate UK data visit the NBN Atlas.Map Help



The hydroid forms bushy, densely branched, 'tree-like' tufts, 2 -5 cm in height. The main stem is a dark horn in colour and composed of multiple tubes near the base of the colony (polysiphonic), becoming single tubed branches towards the edge of the colony. Each single branch is ringed at its base (or insertion) and bears a polyp at its tip. The polyps are white, rose or chestnut in colour with numerous, alternate, colourless tentacles and a ring of large nematocysts at the base of the polyp body. The mouth is borne on a short, globose projection, the hypostome. Reproductive polyps are borne on short stems at right angles to the branches, and distributed in clusters around the colony.

Recorded distribution in Britain and Ireland

Scattered records from the Norfolk coast, around Ireland and the west coasts of Scotland.

Global distribution



Found on sublittoral hard substrata in tidally swept, sand scoured conditions (Picton & Costello, 1998). Also common on corks and buoys at sea (Hamond, 1957).

Depth range


Identifying features

  • Densely branched, bushy, colony up to 2 -5 cm in height.
  • Main stem a dark horn in colour.
  • Polyps white and naked (athecate).
  • Polysiphonic at least basally

Additional information

Also known as Eudendrium arbuscula (see Hincks, 1868; Allman, 1871-1872; Marques & Vervoort, 1999).

Listed by

- none -


  1. Allman, G.J., 1871-1872. A monograph of the Gymnoblastic or Tubularian hydroids, Vol. I & II. London: Ray Society.

  2. Hamond, R., 1957. Notes on the Hydrozoa of the Norfolk Coast. Journal of the Linnean Society (Zoology), 43, 294-324.

  3. Hayward, P.J. & Ryland, J.S. 1994. The marine fauna of the British Isles and north-west Europe. Volume 1. Introduction and Protozoans to Arthropods. Oxford: Clarendon Press.

  4. Hincks, T., 1868. A history of the British hydroid zoophytes, vol. I & II. London: van Voorst.

  5. JNCC (Joint Nature Conservation Committee), 1999. Marine Environment Resource Mapping And Information Database (MERMAID): Marine Nature Conservation Review Survey Database. [on-line] http://www.jncc.gov.uk/mermaid

  6. Marques, A.C. & Vervoort, W., 1999. Eudendrium arbuscula Wright, 1859 (Cnidaria, Hydrozoa): proposed conservation of the specific name. Bulletin of Zoological Nomenclature, 56, 16-18.

  7. Picton, B.E. & Costello, M.J., 1998. BioMar biotope viewer: a guide to marine habitats, fauna and flora of Britain and Ireland. [CD-ROM] Environmental Sciences Unit, Trinity College, Dublin.


  1. Centre for Environmental Data and Recording, 2018. Ulster Museum Marine Surveys of Northern Ireland Coastal Waters. Occurrence dataset https://www.nmni.com/CEDaR/CEDaR-Centre-for-Environmental-Data-and-Recording.aspx accessed via NBNAtlas.org on 2018-09-25.

  2. NBN (National Biodiversity Network) Atlas. Available from: https://www.nbnatlas.org.

  3. OBIS (Ocean Biodiversity Information System),  2023. Global map of species distribution using gridded data. Available from: Ocean Biogeographic Information System. www.iobis.org. Accessed: 2023-09-30


This review can be cited as:

Tyler-Walters, H., 2007. Eudendrium arbuscula A sea fir. In Tyler-Walters H. and Hiscock K. Marine Life Information Network: Biology and Sensitivity Key Information Reviews, [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 30-09-2023]. Available from: https://www.marlin.ac.uk/species/detail/2097

Last Updated: 14/06/2007