Description: This isopod has a very long body, especially the middle section which is particularly long and cylindrical. The first 4 legs are long and covered in long, dense setae (hairs). They are directed towards the mouth of the animal and used for feeding. The next sets of legs are shorter and adapted to hold on securely. There may be a few tubercles on the body but it is mostly smooth, especially in males. Females usually have two conspicuous tubercles on their back towards their head, and often have several smaller ones on their body. Females reach up to 30 mm while males only reach around 10 mm. They have very long antennae and conspicuous eyes.

Habitat: Usually seen subtidally, clinging to hydroids or other tall sedentary animals.

Distribution: Recorded from all around Britain and Ireland.

Similar Species: Quite a distinctive species, could be potentially confused with Astacilla damnoniensis but closer inspection should make distinguishing easy.

Key Identification Features:

• Isopod with very long body and especially long midsection.
• First 4 legs are long and covered in dense setae.
• Very long antennae.

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

iNaturalist: Astacilla longicornis at iNaturalist World Species Observations database.

GBIF data for Astacilla longicornis

WoRMS: Astacilla longicornis at World Register of Marine Species. Accepted name: Astacilla longicornis (Sowerby, 1806). AphiaID: 119024.

Classification: Biota; Animalia; Arthropoda; Crustacea; Multicrustacea; Malacostraca; Eumalacostraca; Peracarida; Isopoda; Valvifera; Arcturidae; Astacilla