Mesogammaridae Bousfield, 1977

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.