Gamasellus ( Hydrogamasellus) Hirschmann, 1966: 6.
Hydrogamasellus.— Lee, 1970: 110; Karg, 1976 a: 37; 1997: 64; Karg & Schorlemmer, 2009: 79.
Type species: Hydrogamasus antarcticus Trägårdh, 1907, by original designation.
Diagnosis (adult female). Epistome with an anteromedian extension wider at the base, acute or bifurcate distally, with one to several spines next to the median level of the margins. Podonotal and opisthonotal shields fused [separated in H. crozetensis (Richters, 1907) and H. racovitzai (Trouessart, 1903)]. Podonotal region of dorsal shield with 18–22 pairs of setae. Dorsal and ventrianal shields not fused. Venter with one pair of presternal platelets; sternal shield not fused to endopodal shields laterad of coxae III and IV; setae st 1 – st 4 in longitudinal line or st 4 slightly laterad of st 1 – st 3. Peritreme straight and extending anteriorly to level between middle region of coxa III and coxa I. Peritrematic shield fused posteriorly to exopodal shield near coxa IV, with the connection wider or narrower than the peritreme. Genu I with 13 setae. Pretarsus I pedunculate and about half as long as other pretarsi.