Description: This isopod has an elongate oval 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 with two segments and one partial suture. It is slightly keeled towards the back and has one large point in the centre with a less pronounced point on either side, making it almost tridentate. Males grow 10-30 mm long while females reach 10-18 mm. It is usually green or brown with some white markings, but may rarely be uniform in colour. Females may be darker than males. They have two long antennae and small eyes.

Habitat: Usually an offshore species but occasionally be found amongst algae or washed up on shore with drift seaweed, sometimes in huge numbers.

Distribution: Recorded all around Britain and Ireland.

Similar Species: Could be confused with some other Idotea species. Careful inspection of features, especially the shape of pleotelson can help distinguish.

Key Identification Features:

• Pleotelson slightly keeled towards rear and almost tridentate.
• Usually green or brown with white markings.

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

iNaturalist: Idotea baltica at iNaturalist World Species Observations database.

WoRMS: Idotea baltica at World Register of Marine Species. Accepted name: Idotea balthica (Pallas, 1772). AphiaID: 119039.

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