This beautiful sea slug is rare in Northern Ireland, where it feeds on solitary hydroids.

In brief

• It lives on sandy seabeds or on its prey, the hydroid Corymorpha nutans
• It can only be seen by diving
• This species is rare in Northern Ireland and it has not been found anywhere else in the whole of Ireland. Northern Ireland is the stronghold for Britain and Ireland
• Threats to this species are unknown, as there is little knowledge of the current populations in Britain and Ireland.

Species description: Cumanotus beaumonti has a translucent reddish body and flesh-coloured numerous cerata with pale tips arranged in transverse rows. The back of the body is covered with speckles of gold pigment, and concentrated into patches on the head. The head is broad and bears a pair of finger-like oral tentacles. It is up to 25 mm in length, with a broad foot.

Life cycle: As with all nudibranch sea slugs, Cumanotus beaumonti is a hermaphrodite. Spawning occurs in May, with the spawn taking the form of coils of two to four turns of white jelly, attached to the sand by a long, string-like stalk, covered in sand grains.

Similar species: There are no closely similar species, although it could be superficially confused with Facelina bostoniensis. However, Facelina bostoniensis has long oral tentacles, annulate rhinophores and lacks the gold-flecked pigmentation.

How to see this species: This species has only been found off Rathlin Island in 8-20 m, south-east of Kilkeel in 20 m, and off Cranfield Point, Carlingford Lough in 20 m. It can be seen either crawling on a sea-bed of medium sand, or at the tops of and devouring the stalks of the solitary athecate hydroid Corymorpha nutans. The animals are vigorous swimmers, moving through the water by repeated violent vertical movements of the cerata or flexing of the body.

Current status: Rare. This species is not often recorded in Northern Ireland, but the Northern Irish records are the only known records for the island of Ireland. There are only a few scattered records from Britain, making Northern Ireland the stronghold for this species for both Britain and Ireland. It is only known with certainty elsewhere from Norway, western Scotland and Plymouth.

Why is this species a priority in Northern Ireland?

• Criterion 3: Rare or restricted range – rare breeding species confined to 5 hectads or less (based on expert judgement)
• Criterion 4: NI stronghold or endemic – both stronghold range/population and designation as ‘endemic’ subject to expert judgement.

Threats: Threats to this species are unknown, as there is little knowledge of the current populations in Britain and Ireland.

Action: Records of new sites for this species, with details of habitat and population are always valuable. Observations with a photograph can be recorded using iNaturalist, find the MBDP-NI iNaturalist project here.

Alternatively, records can be sent to CEDaR, National Museums Northern Ireland, 153 Bangor Road, Cultra, Holywood, County Down, BT18 0EU. Tel 028 9039 5257, e-mail cedar.records@nationalmuseumsni.org, or via the online portal.

Objectives:

• Perform targeted surveys to ascertain the current status of the species in Northern Ireland.
• Ensure that the current population level is maintained through protection of suitable habitat.

Conservation:

• Rathlin Island is a Marine Protected Area with multiple designations.

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

iNaturalist: Cumanotus beaumonti at iNaturalist World Species Observations database.

WoRMS: Cumanotus beaumonti at World Register of Marine Species. Accepted name: Cumanotus beaumonti (Eliot, 1906). AphiaID: 139431.

Classification: Biota; Animalia; Mollusca; Gastropoda; Heterobranchia; Euthyneura; Ringipleura; Nudipleura; Nudibranchia; Cladobranchia; Fionoidea; Cumanotidae; Cumanotus

Previous species

Next species

Adapted from text by Dr Julia Nunn (2026). Cumanotus beaumonti. (Eliot, 1906). [In] Priority species, Marine Biodiversity Portal NI. https://www2.habitas.org.uk/marbiop-ni/priorityaccounts.php?item=W15200. Accessed on 2026-09-13