Astacilla intermedia (Goodsir, 1841)
Astacilla species are distinctive marine isopods that are mostly sublittoral but can occasionally turn up in the intertidal zone. They have long antennae with extended 4th and 5th segments, an elongated middle pereon segment, short walking legs on pereon segments 5 to 7, and usually with adapted, setose legs on pereon segments 1 to 4 that are directed towards the mouth for feeding. The pereon segments are typically ornamented with tubercles and/or spines.
A. intermedia has a double row of tubercles down each side of its body, most prominently on the 1st to 3rd and 5th to 7th pereon segments, and has a bulging abdomen.
Astacilla species are filter feeders that typically cling to seaweed, echinoderms, coelenterates, etc.
This species occurs sublittorally.
Naylor, E. & A. Brandt. 2015. Intertidal Marine Isopods. Synopses of the British Fauna (New Series), No. 3. Field Studies Council, for The Linnean Society of London.