Length to 21 mm (Hyperia spinigera 1). Pereonites relatively long, head slightly shorter than, or equal to, first two pereonites combined. Mandibular palp with subequal ART, incisor with about 15 teeth in adults, in juveniles or adolescents teeth only on molar half of incisor. Inner lobe of MXP longer than outer lobes in juveniles/adolescents, shorter than outer lobes in adults (Hyperia spinigera 2). Apical ART of P I and II with numerous strong setae (Hyperia spinigera 3), these P chelate (P I - weakly chelate). P III and IV similar, sometimes with cluster of setae on posterior distal corner of ART 2 (Hyperia spinigera 4). ART 3 and 4 of P III and IV unarmed in juveniles/adolescents, with uniformly short, closely spaced setae in adults. These setae appear during one molting (Thurston, 1977). P V-VII robust. Anterodistal corner of ART 2 of P V-VII with cluster of setae, other ART unarmed. Posteroventral corners of epimeral plates more or less pointed, or between pointed and rounded (especially in epimeral plate I). Posterior margin of epimeral plate III strongly convex. Basipodites of UR II and III with small triangular processes on inner distal corner, in UR II process may be dentate. Basipodite of UR III broad. Telson about twice as short as basipodite of UR III, or slightly less. Change of "juvenile/adolescent" and "adult" characters may be not simultaneous, and specimens with "mosaic" characters (for example with unarmed P III-IV and short inner lobe of MXP) may be found (Vinogradov, 1990b). Some individuals may become adult without acquiring "adult" characters. Some authors consider Hyperia spinigera, in our opinion a valid and distinct species, a junior synonym of Hyperia galba (Montagu, 1813). This explains records of "Hyperia galba" in the Southern hemisphere, where this species is actually absent (Bowman, 1973). Another southern hyperiid "species", Hyperia antarctica Spandl, 1927, is effectively a junior synonym of Hyperia spinigera; the name "Hyperia antarctica" comprising animals with juvenile characters (Thurston, 1977; Vinogradov, 1990b). In the Atlantic Ocean Hyperia spinigera is often associated with the scyphomedusan Periphylla periphylla (Thurston, 1977).