Jaera (Jaera) albifrons Leach, 1814
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 albifrons (sensu stricto) is one of the 'albifrons' group of species (along with Jaera forsmani, 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 an obvious bulge on the distal end of the carpus of the male 6th and 7th pereopods. Males up to 2.4mm, females up to 5.0mm. See further the Identifying Jaera page.
Distribution and Habitat
Common around Britain and Ireland under stones in shallow water at HWN, though it is unclear how many older records refer to J. albifons (s.s.) rather than the 'albifrons' group as a whole.
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.