ZENKEVITCHIIDAE Sidorov, 2018

Sidorov, Dmitry, Taylor, Steven J., Sharina, Svetlana & Gontcharov, Andrey, 2018, Zenkevitchiidae fam. nov. (Crustacea: Gammaroidea), with description of new subterranean amphipods from extremely deep cave habitats, Journal of Natural History (J. Nat. Hist.) 52 (23 - 24), pp. 1509-1535 : 1517

Order AMPHIPODA Latreille, 1818

Family ZENKEVITCHIIDAE Sidorov fam. nov.

Type genus and species

Zenkevitchia admirabilis Birstein, 1940 , original designation.

Diagnostic description

Amphipods with troglomorphic traits (anophthalmy and pigment reduction), habitus reveals two morphotypes 1 – a ‘stream ecomorph’ (with short limbs adapted to fast-moving cave waters) and a ‘lake ecomorph’ (with elongated urosomal segments and limbs adapted to living in a cave lakes); mouthparts scraper-like or filtrative. Appendages elongate or stout but more setose than spiny, modified for swimming or burrowing. Rostrum vestigial; lateral cephalic lobe mammilliform (with or without recess); inferior antennal sinus moderate, rounded. Coxal plates I–IV of different shapes, but always deeper than broad; plate IV with excavation. Antenna I longer than antenna II, accessory flagellum well developed, aesthetascs if present are very small; peduncular articles of antenna II densely setose with long bunches of setae, gland cone of variable length (can reach half of pedunclar article IV), calceoli absent. Maxilla I, outer plate with variable extent of spines which may be modified in shape and number, namely: ‘scraper-type’ with 12–22 multi-toothed, comb-like spines, and ‘filtrationtype’ with 23 to 105–200 multi-toothed, sickle-shaped and comb-like spines; palps clearly asymmetric or sub-symmetric, somewhat reduced. Mandibles, incisor process with 4 or 5 teeth, right lacinia mobilis bifurcate with several denticles, between lacinia and triturative molar a row of serrate spines (one or two may be modified); palp well-developed, article III (distal) with groups of A-, B-, D- and E-setae (C-setae absent). Lower lips with or without inner lobes. Remaining mouth parts (upper lip, maxilla I and maxilliped) ordinary, without of obvious peculiarities. Gnathopods I and II relatively small, with propodus slightly larger than corresponding coxa; palmar angles of both gnathopods well-defined or undefined but with mid-palmar spines; propodi with multiple rows of short, bifid, robust setae along palmar margin, each bearing a rows of notched, strong palmar spines; dactyli with 1 seta along outer margin, nails of various lengths. Pereopods V–VII bases distinctly broader in proximal part (sometimes posterior margins with well-developed postero-proximal lobes); inner margin of dactyli of pereopods III–VII with 1 stiff seta. Pleopods I–III ordinary, with 2 coupling setae (retinacula), each accompanied by 1 or 3–4 stiff setae. Urosomites with dorsolateral groups of spines. Uropod III biramous, densely setose in males, inner ramus (endopodite) shorter than outer ramus, outer ramus (exopodite) normally one-segmented. Telson deeply or entirely cleft, lobes with apical spines. Coxal gills II–VII stalked, triangular or sacciforme, largest on gnathopod II, successively smaller on pereopods III to VII, gill VII the smallest.