Northern Ireland's Priority Species

Arachnanthus sarsiArachnanthus sarsi


Arachnanthus sarsi Carlgren, 1912

A rare and distinctive anemone living in subtidal sediments. In Northern Ireland it only occurs around Rathlin Island, is declining, and is vulnerable to disruption of its habitat by fishing.

In brief

  • Can be found on the southern coast of Rathlin Island
  • Lives in sublittoral sands, gravels and shelly muds
  • Can be found throughout the year
  • Listed as a priority because of its rarity and possible decline
  • Main threats likely to come from mobile fishing gear and impacts on its habitat.

Species description
A large burrowing anemone, dwelling in parchment-like tubes in mud, sand or shelly mud. When extended out from the tube it may be up to 200mm in height. It has a conspicuous and large fringe of about 30 long outer tentacles which have vaguely delineated bands of different shades, and a similar number of shorter, fine, inner or labial tentacles that come together at their tips to form a distinctive cone. The species is suspected by some of being nocturnal, which may explain to some extent the scarcity of records.

Life cycle
No information is currently available on the life cycle of this species in Northern Ireland, or in adjacent waters.

Similar species
Cerianthus lloydii is similar, but lacks the distinctive cone. Some researchers consider Arachnanthus sarsi may be conspecific with Arachnactis albida.

How to see this species
Arachnanthus sarsi is only recorded in Northern Ireland on Rathlin Island, in Church Bay. Elsewhere it can be found in western Scotland waters, and off Malin Beg, Donegal. Individuals are found buried in mud, sand, and shelly muds, generally from 1036m depth.

Current status
In Northern Ireland it is known only from one section of coast on Rathlin Island. The species has no legal protection.

Why is this species a priority in Northern Ireland?
Arachnanthus sarsi is extremely rare in Northern Ireland and may be declining. It is also scarce throughout the rest of the UK and Ireland.

Threats/Causes of decline
No specific reasons for the decline have been identified; however, the species is likely to be vulnerable to disturbance of its seabed habitat by mobile fishing gear, and its only known location has been subject to this type of fishing.

Conservation of this species

Current action
Survey work is being conducted throughout Northern Ireland waters (including the north coast) by Northern Ireland Environment Agency for this and other species and habitats generally.

Rathlin Island and its waters are designated a Special Area for Conservation under the EU Habitats Directive.

There is no Species Action Plan for Arachnanthus sarsi, but it is listed as a UK Priority species. Relevant Habitat Action Plans include UK Sublittoral Sands and Gravels, and Inshore Sublittoral Sediment plans, and the NI Sublittoral Sands and Gravels Plan. This has the following actions:

  • maintain the extent of a representative range of sublittoral sands and gravel habitats and associated communities in Northern Ireland
  • maintain the condition of a representative range of sublittoral sands and gravel habitats and associated communities in Northern Ireland.

Proposed objectives/actions

  • Maintain the only known population of this species in a viable state
  • Maintain the range of this species
  • Establish database to determine trends in conservation status
  • Identify new sites where possible.

What you can do
Records of new sites for this species, with details of habitat and population are always valuable. Send these to CEDaR, National Museums Northern Ireland, 153 Bangor Road, Cultra, Holywood, County Down, BT18 0EU. Tel 028 9039 5257 or e-mail [at] If you are a diver, and interested in becoming involved in recording marine life in Northern Ireland through the Seasearch project, contact Claire Goodwin at claire.goodwin [at] or look at the web site (Northern Ireland web pages).

Further information

Encyclopedia of Marine Life

NBN Gateway

Marine Life Information Network

Howson, C.M. and Picton, B.E. (ed.) (1997). The species directory of the marine fauna and flora of the British Isles and surrounding seas. Ulster Museum and The Marine Conservation Society, Belfast and Ross-on-Wye. Belfast: Ulster Museum. [Ulster Museum publication, no. 276.].

JNCC (Joint Nature Conservation Committee) (1999). Marine Environment Resource Mapping and Information Database (MERMAID): Marine Nature Conservation Review Survey Database. [on-line] Peterborough: Joint Nature Conservation Committee.

NBN (National Biodiversity Network) (2002). National Biodiversity Network Gateway. Environmental Information Centre and Centre for Ecology and Hydrology, Monks Wood, and the Joint Nature Conservation Committee, Peterborough.

Picton, B. E. and Manuel, R.L. (1985). Arachnanthus sarsi Carlgren, 1912: a redescription of a cerianthid anemone new to the British Isles. Zoological Journal of the Linnean Society 83: 343-349.

Wilson, E. (2007). Arachnanthus sarsi. A sea anemone. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 26/03/2008].

Text written by:
Allen & Mellon Environmental Ltd.