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. dilatata has a pair of large processes in the middle of the 4th pereon segment.
Distribution and Habitat
Astacilla species are filter feeders that typically cling to seaweed, echinoderms, coelenterates, etc. A. dilatata is a sublittoral species that may occur in shallow water around Britain and Ireland, especially in the north.
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.