Erato voluta is a rare mollusc in Northern Ireland, which can only be seen by diving.

In brief

• The species is found off Rathlin Island on hard substrates, and can only been seen by diving
• It is rare in Northern Ireland, and has not been seen here since 1984. It has been found living at a number of scattered locations in Ireland

Species description: The shell is slightly translucent, whitish and glossy with 3-4 whorls of which the last occupies 80-85 per cent of the height. The thick outer lip is inturned, with 15-18 ridge-like teeth on its inner edge, normally white, sometimes brownish and pink. It is up to 12 mm high, with a truncated apex, and relatively large but narrow aperture. The animal is white, speckled with brown, red, orange and yellow. The mantle is drawn out to form dark lobes with yellow tubercules over the shell, and siphon in a basal canal.

Life cycle: This species has separate sexes, with planktonic larvae present in the spring and summer. Most of the life cycle is unknown.

Similar species: There are three similar species in Northern Ireland waters: Simnia patula, Trivia arctica and T. monacha. Simnia patula is yellow, with a mantle of yellow striped with black, and is found on dead men's fingers Alcyonium digitatum. Trivia spp. have ridged shells (unlike Erato) except for juveniles. The juveniles have very thin shells, with no spire in mature shells, whereas Erato voluta has a thick shell and a short spire.

How to see this species: Erato voluta has only been found living off the coast of Rathlin Island in Northern Ireland, in waters deeper than 20 m, during the summer months of 1983 and 1984. Shells have been found on the strands at Portstewart and Magilligan. It lives on hard substrates, with pockets of sediment, and associates with ascidians which form its food.

Current status: This species is rare in Northern Ireland, with live records from only two sites off Rathlin Island, and has not been seen since 1984. It has only certainly been found alive elsewhere in Ireland in Galway Bay. Although distributed around most of Britain, it is largely absent from the eastern waters of England, and is rarely found. The species is generally distributed from the Mediterranean to Norway in 20-100 m.

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: Possible threats to Erato voluta are unknown, as so little is known about the biology and ecology of this species.

Action: 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.records@nationalmuseumsni.org, or via the online portal. You can also record observations including a photograph using iNaturalist, find the MBDP-NI iNaturalist project here.

Objectives:

• Perform targeted surveys to ascertain the current status of the species in Northern Ireland
• If refound, ensure that the population is maintained.

Conservation: All Northern Ireland sites where live animals have been recorded lie within Rathlin Island Marine Conservation Zone.

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

iNaturalist: Erato voluta at iNaturalist World Species Observations database.

WoRMS: Erato voluta at World Register of Marine Species. Accepted name: Erato voluta (Montagu, 1803). AphiaID: 139761.

Classification: Biota; Animalia; Mollusca; Gastropoda; Caenogastropoda; Littorinimorpha; Velutinoidea; Eratoidae; Erato