Jaera (Jaera) forsmani Bocquet, 1950
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 forsmani is one of the 'albifrons' group of species (along with Jaera albifrons, Jaera ischiosetosa and Jaera praehirsuta), all of which have a T-shaped male preoperculum. It can be distinguished from the other species by the presence of a well-developed carpal spine on the male 6th and 7th pereopods and by a sparse covering of curved setae on the propodus, carpus and merus of male pereopods 1-4. Males up to 3.4mm, females up to 6.0mm.
Distribution and Habitat
Rather sparsely distributed, found especially under stones between HWN and LWS on well-drained shores in western Britain and Ireland.
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.