Jaera praehirsuta Forsman, 1949
Jaera are small, ubiquitous intertidal marine isopods which can be identified to species by the examination of male reproductive structures (specifically the preoperculum) and pereopods. Preopercula can be examined using a binocular dissecting microscope, but examination of pereopods is best done using a compound microscope at low power.
Jaera praehirsuta is one of the 'albifrons' group of species (along with Jaera albifrons, Jaera forsmani and Jaera ischiosetosa), all of which have a T-shaped male preoperculum. It can be distinguished from the other species by the presence of a dense covering of long, curved setae on the propodus, carpus and merus of male pereopods 1-4. The carpal spine on pereopod 6 is poorly developed, in contrast with that of J. forsmani. Males up to 3.0mm, females up to 4.5mm. See further the Identifying Jaera page.
Not well reported but likely to be common and widespread around Britain and Ireland. Mostly among fucoid algae up to HWN.
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.