Description: This isopod has a short, stout body with obvious segments aside from the posterior of the animal where the segments are fused. Here the pleon and telson fuse to form the pleotelson which is not keeled and is broadly rounded at the tip. Males grow 4-11 mm long while females reach 7-10 mm. It is usually a dark purple-brown with white diamond-shaped patches or striped, as well as some white markings along dorsal edge. Females are usually darker in colour than the males. All legs are quite robust. Males in these species have dense cilia on their antennae.

Habitat: Usually found intertidally amongst mussels, barnacles or fucoids on exposed shores. Colouration can mean they are well-hidden amongst barnacles.

Distribution: Scattered records from all around Britain and Ireland.

Similar Species: Could be confused with other Idotea species. This is more short, stout isopod with a broadly rounded pleotelson.

Key Identification Features:

• Short, stout body.
• Pleotelson is broadly rounded.
• Usually dark purple-brown with white markings.
• Males have dense cilia on antennae.

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

iNaturalist: Idotea pelagica at iNaturalist World Species Observations database.

GBIF data for Idotea pelagica

WoRMS: Idotea pelagica at World Register of Marine Species. Accepted name: Idotea pelagica Leach, 1816. AphiaID: 119050.

Classification: Biota; Animalia; Arthropoda; Crustacea; Multicrustacea; Malacostraca; Eumalacostraca; Peracarida; Isopoda; Valvifera; Idoteidae; Idotea