A burrowing sea cucumber known only from Strangford Lough in Northern Ireland, living buried in muddy sands. Its habitat has been heavily impacted by fishing.

In brief

• Found near Dunnyneill Island, Strangford Lough
• Lives buried in muddy sands
• Likely to be visible, through careful searching, throughout the year
• Only one location known, and the species has probably declined there
• Main cause of decline is probably bottom trawling and dredging.

Species description: A rather wormlike sea cucumber (holothurian) ranging from 10 to 30cm in length. It has a pinkish, transparent skin and body, and the five longitudinal muscles within show clearly. It has twelve pinnate (feather-like) tentacles, each of which has 8-11 pairs of digits, and these are somewhat longer towards the end of the tentacle. The animal lacks tube feet. The spicules (skeletal structures) are anchor in form, with pear-shaped plates.

Life cycle: No information is currently available for this in Northern Ireland.

Similar species: All the British synaptids are similar, and need to be sorted by close examination of the tentacles and spicules (skeletal structures in the body wall).

How to see this species: The only location in Northern Ireland where it may be found is to the south-east of Dunnyneill Island in Strangford Lough, and the only location elsewhere in Ireland is Kilkieran Bay. It occurs buried in sublittoral muddy sands.

Current status: There is only one known location in Northern Ireland, and one in the Republic of Ireland, thus Northern Ireland may hold about half the Irish population. It is recorded sparsely around a number of northern locations in Britain. The species has no legal protection.

Why is this species a priority in Northern Ireland? The species is rare, being only known from one location, and may be in decline.

Threats: The only known location has been heavily impacted by bottom fisheries in Strangford Lough, causing disruption and loss of habitat. The species is also recorded as being sensitive to industrial waste and dumping.

Action:

• Maintain the number of viable populations of the species
• Maintain the range of the species
• Establish appropriate management of its only known site, and of any others that are discovered
• Monitor population in Strangford Lough.

Objectives: 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 cedar.info [at] nmni.com. 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] gmail.com or look at the web site www.seasearch.org.uk (Northern Ireland web pages).

Conservation: 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.

Strangford Lough has been designated a Special Area for Conservation under the EU Habitats Directive, and is a Marine Nature Reserve. Following concerns about the impact of fishing on key features of the lough, a study on ecological change was conducted in 2004, and following this a project to restore the Modiolus modiolus community has commenced. Use of mobile fishing gear in the lough has been banned.

There is no Species Action Plan for this species, but the relevant UK Habitat Action Plans include:

• Modiolus modiolus beds
• mud habitats in deep water
• inshore sublittoral sediments.

The relevant Northern Ireland Habitat Action Plans are for Inshore Sublittoral Sediment and for Mud Habitats in Deep Water. The latter contains the following actions:

• where appropriate, maintain the extent of mud habitats in deep water and associated animal communities
• maintain representative examples of mud habitats in deep water and their associated animal communities which exhibit minimal anthropogenic influences
• where appropriate, enhance the extent and condition of nationally important mud habitats in deep water in Northern Ireland.

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

iNaturalist: Leptosynapta bergensis at iNaturalist World Species Observations database.

WoRMS: Leptosynapta bergensis at World Register of Marine Species. Accepted name: Leptosynapta bergensis (Östergren, 1905). AphiaID: 124462.

Literature:

Hiscock, K., Langmead, O. and Warwick, R. (2004). Identification of seabed indicator species from time-series and other studies to support implementation of the EU Habitats and Water Framework Directives. Report to the Joint Nature Conservation Committee and the Environment Agency from the Marine Biological Association. Plymouth: Marine Biological Association. JNCC Contract F90-01-705. 109 pp.

Picton, B.E. and Morrow, C.C. (2007). [In] Encyclopedia of Marine Life of Britain and Ireland. http://www.habitas.org.uk/marinelife/species.asp?item=ZB5240.

Southward, E.C. and Campbell, A.C. (2006). [Echinoderms: keys and notes for the identification of British species]. Synopses of the British fauna (new series), 56. Field Studies Council: Shrewsbury, UK. ISBN 1-85153-269-2. 272 pp.

Classification: Biota; Animalia; Echinodermata; Echinozoa; Holothuroidea; Paractinopoda; Apodida; Synaptidae; Leptosynapta

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Allen & Mellon Environmental Ltd. (2026). Leptosynapta bergensis. (Ostergren, 1905). [In] Priority species, Marine Biodiversity Portal NI. https://www2.habitas.org.uk/marbiop-ni/priorityaccounts.php?item=ZB5240. Accessed on 2026-07-28