Description: The most commonly recorded isopod, males reach a larger size than females (male range 5-20 mm, female range 6-13 mm). Colouration is usually a uniform brown, red or green according to the colour of the seaweed that they are on. Occasionally they have some white markings which, although they can vary, are often in a line down the centre of the body. Tail narrows to a sharp point, with concave sides.

Habitat: Found between the tide marks on most coasts, although they are absent from very exposed coasts. Often found hiding in or amongst seaweeds: Fucus, Ascophyllum, Cladophora and Polysiphonia are all common, however they can be found on a large range of species.

Distribution: Recorded from all coasts around Britain and Ireland, aside from very exposed areas.

Similar Species: There are other isopods this could be confused with, especially other Idotea species.

Key Identification Features:

• Often uniformly green, red or brown.
• Sometimes with white markings, most commonly a line down the centre if white markings are present.
• Tail narrows to a sharp point, with concave sides.

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

iNaturalist: Idotea granulosa at iNaturalist World Species Observations database.

WoRMS: Idotea granulosa at World Register of Marine Species. Accepted name: Idotea granulosa Rathke, 1843. AphiaID: 119044.

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