A little-known hermit crab whose only known Irish location is Rathlin Island.

In brief

• Found east of Doon Point and off Ushet Point, Rathlin Island
• Habitat is intertidal and shallow subtidal muds and sands with eelgrasses
• Can be found throughout the year
• A priority species since Northern Ireland holds the only known Irish locations
• Main threats likely to come from deteriorating water quality and shallow water dredging.

Species description: A small grey-brown hermit crab with a carapace (upper shell) of about 5mm length. Its hairy claws are about the same length (not always the case with crabs) but the right claw is much thicker and more robust than the left. The eyestalks are long and quite thick, and between them the margin of the carapace is extended into a short point, or rostrum.

Life cycle: The life cycle is poorly known, but in the British Isles, planktonic larvae have been recorded from March to November. In Italy, females bearing eggs have been recorded between March and September.

Similar species: None.

How to see this species: Cestopagurus timidus can be found in intertidal and shallow sublittoral muds and soft sands, especially in or around eelgrass and algal beds. It has been recorded on Rathlin Island to the east of Doon Point and off Ushet Point, and in the Clyde and the Scilly Isles. Further afield, it has been recorded on the Atlantic coasts of mainland Europe, and in the Mediterranean.

Current status: This species is known from only two sites in Northern Ireland, both on Rathlin, and these represent 100 per cent of the known Irish population. It has no legal protection.

Why is this species a priority in Northern Ireland? The species is rare and possibly declining, and there is a shortage of data on its status. It is also noted as scarce in the rest of the UK and Ireland.

Threats: The species and its habitat are vulnerable to shallow water dredging, and because of the relatively sheltered, sometimes partially enclosed nature of its sites, it would be vulnerable to deterioration of water quality and eutrophication.

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

iNaturalist: Cestopagurus timidus at iNaturalist World Species Observations database.

WoRMS: Cestopagurus timidus at World Register of Marine Species. Accepted name: Cestopagurus timidus (Roux, 1830). AphiaID: 107226.

Classification: Biota; Animalia; Arthropoda; Crustacea; Multicrustacea; Malacostraca; Eumalacostraca; Eucarida; Decapoda; Pleocyemata; Anomura; Paguroidea; Paguridae; Cestopagurus