Type genus. Mesogammarus Tzvetkova, 1965.
Diagnostic description. Body laterally compressed. Eyes well developed or absent, if present then ovoid or reniform. Antennae 1–2 calceoli gammarid (type 1). Antenna 1 subequal in length to, or longer than antenna 2; peduncular article 1 subequal to, or longer than article 2; article 2 longer than article 3; article 3 shorter than article 1; peduncular articles 1–2 not geniculate; accessory flagellum short. Antenna 2 peduncular article 1 enlarged, bulbous. Mandible molar triturative; palp symmetrical. Maxilla 1 basal endite setose along medial margin; palps symmetrical. Maxilla 2 basal endite without oblique setal row. Labium inner lobes vestigial or absent. Coxal gills on pereopods 2–6, not stalked; sternal gills absent; sternal blisters absent; oostegites fringing setae simple. Gnathopod 1 subchelate; similar in males and females (not sexually dimorphic); similar in size to, or larger (or stouter) than gnathopod 2; propodus palm with row or rows of simple or bifid robust setae along palmar margin. Gnathopod 2 subchelate; dissimilar in males and females (sexually dimorphic); carpus not produced along posterior margin of propodus, projecting between merus and propodus. Pereopods 3–4 not sexually dimorphic. Pereopod 4 without posteroventral lobe. Pereopod 5 shorter than pereopod 6; coxa with large anteroventral lobe or with small anteroventral lobe. Pereopod 7 longer than pereopod 5. Pleonites 1–3 without dorsal carinae. Urosomites 1–3 free; with slender or robust dorsal setae. Urosomite 1 with or without large distoventral robust seta. Urosomite 2 with pair of dorsal concavities each with 1–3 small setae. Uropod 1 with or without 1 or 2 basofacial robust setae. Uropod 3 not sexually dimorphic; biramous, without plumose setae; endopod minute, shorter than or subequal to exopod. Telson moderately cleft or notched; dorsal or lateral robust setae present; apical robust setae present.
Habitat. Marine, intertidal epigean.
Included genera. Mesogammarus Tzvetkova, 1965; Paramesogammarus Bousfield, 1979.
Distribution. North Pacific.