Squirrel's tail hydroid (Sertularia argentea)

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A sea fir forming three-dimensional, cypress tree-shaped colonies typically up to 15 cm in length but may be up to 30 cm. The colony is golden-brown in colour. The main stem is flexible, monosiphonic, sometimes forking, and there are often several stems grouped together. The side branches are usually shorter and uniform in length, appearing all around the main stem, giving the appearance of a bottle-brush. Internodes of the main stem bear polyps in tubular chitinous cups (hydrothecae) directed outwards. The colony bears both male and female reproductive polyps (gonothecae).

Recorded distribution in Britain and Ireland

Widespread around British Isles and east coast of Ireland. Less common on the east coast of Scotland and south-eastern coast of England.

Global distribution

Sertularia argentea is recorded in the North Atlantic and adjacent parts of the Arctic Ocean, from the Shetland Isles south to the Biscay coast of France and northern Spain in the east and from Nova Scotia to North Carolina in the west. It is also recorded in the North Pacific from Alaska to California.


Sertularia argentea inhabits shallow pools on sand flats and mudflats, and sandy substrata usually on pebbles, shells, rocks, or other hard objects. It is occasionally found on algal stems. It is commonly found in areas subject to strong water movement from either tidal streams or wave action, and is abundant in narrows and rapids with tidal streams of more than three knots. Sertularia argentea is less common in silty and brackish localities.

Depth range

Recorded in depths of 0-30 m

Identifying features

  • Colony comprising of erect, long and bushy stems, with branches uniform in length.
  • Branches arise from all sides of stem with ‘bottle brush’ effect.
  • Golden-brown in colour.
  • Hydrothecae rim with two unequal cusps.
  • Gonothecae are borne abundantly on side branches.
  • The male and female gonothecae are equal in size.

Additional information

Sertularia argentea is similar to Sertularia cupressina and their status as separate species is questioned (see Cornelius, 1979). The shape of the hydrothecae and gonothecae is slightly different between the two species but a microscope is needed to confirm (Porter, 2012).

Listed by

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  1. Cornelius, P.F.S. 1979. A revision of the species of Sertulariidae (Coelenterata: Hydroida) recorded from Britain and nearby seas. Bulletin of the British Museum (Natural History) Zoology

  2. Cornelius, P.F.S., 1995b. North-west European thecate hydroids and their medusae. Part 2. Sertulariidae to Campanulariidae. Shrewsbury: Field Studies Council. [Synopses of the British Fauna no. 50]

  3. Hancock, D.A. Drinnan, R.E. Harris, W.N. 1956. Notes on the biology of Sertularia argentea L. Journal of the Marine Biological Association of the United Kingdom, 35, 307-325. DOI https://doi.org/10.1017/S0025315400010158

  4. Hayward, P., Nelson-Smith, T. & Shields, C. 1996. Collins pocket guide. Sea shore of Britain and northern Europe. London: HarperCollins.

  5. Porter, J., 2012. Seasearch Guide to Bryozoans and Hydroids of Britain and Ireland.   Ross-on-Wye: Marine Conservation Society.



    This review can be cited as:

    Lloyd, K.A., 2021. Sertularia argentea Squirrel's tail hydroid. 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 21-04-2024]. Available from: https://www.marlin.ac.uk/species/detail/2346

    Last Updated: 30/09/2021