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 nordmanni is a distinctive species with a relatively large, rounded, flattened body fringed by numerous setae. The pointed, neck-tie shaped male preoperculum is diagnostic. Males up to 4.5mm, females up to 3.5mm.