Description: A small pea crab that lives inside bivalves (e.g. oysters, mussels, clams) and occasionally also in some ascidians. The carapace is smooth, in females it is soft, translucent and the organs are visible as well as the gonads. In males it is hard and yellow-grey with patches of brown. Females are smaller than males, growing to around 6 mm while males can reach 13 mm carapace length. They have tiny antennae. The pincers are equal in size, and smooth like the carapace. The walking legs are slender and end in a short, curved point. The area between the eyes is often curved downwards and the eyes and eye orbits are relatively small, especially in females.

Habitat: Reported from lower shore to around 45 m depth, usually found within bivalves (e.g. Arctica, Mytilus, Modiolus, Acanthocardia, Venus, %Lutraria%, etc.) and occasionally ascidians.

Distribution: Found on most coasts of Britain and Ireland where suitable bivalves (or ascidians) are present. Seems less common in north of Scotland than in other areas.

Similar Species: Could be confused with Nepinnotheres pinnotheres.

Key Identification Features:

• A small pea crab (M 13 mm; F 6 mm) that lives inside bivalves or occasionally ascidians.
• Smooth carapace, soft and translucent in females and hard and yellow-grey in males, often with brown patches.
• Tiny antennae and small eyes.
• Slender walking legs ending in a short, curved point.

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

iNaturalist: Pinnotheres pisum at iNaturalist World Species Observations database.

GBIF data for Pinnotheres pisum

WoRMS: Pinnotheres pisum at World Register of Marine Species. Accepted name: Pinnotheres pisum (Linnaeus, 1767). AphiaID: 107473.

Classification: Biota; Animalia; Arthropoda; Crustacea; Multicrustacea; Malacostraca; Eumalacostraca; Eucarida; Decapoda; Pleocyemata; Brachyura; Eubrachyura; Thoracotremata; Pinnotheroidea; Pinnotheridae; Pinnotherinae; Pinnotheres