Crangonyctidae Bousfield, 1973

Palatov, Dmitry M. & Marin, Ivan N., 2023, Diversity of the Caucasian genus Diasynurella Behning, 1940 (Amphipoda: Crangonyctidae) with description of four new species, Arthropoda Selecta 32 (1), pp. 23-55 : 24-25

Family Crangonyctidae Bousfield, 1973

Diasynurella Behning, 1940

INCLUDED SPECIES. Diasynurella wachuschtii Behning, 1940 (the type species), D. kiwi Marin et Palatov sp.n., D. dzhamirzoevi Palatov et Marin sp.n., D. cavatica Palatov et Marin sp.n. and D. khalabensis Palatov et Marin sp.n.

DIAGNOSIS. Size relatively small, up to 3–4.5 mm in females, which are larger than males. Body smooth, not pigmented (troglomorphic), urosomites partly fused, with marked suture between segments, without dorsal spines. Urosomite I free, urosomites II and III completely fused or free. Head without rostrum, lateral lobe rounded anteriorly; black eye (ommatidia) or yellow spots absent on head. Antenna I longer than antenna II; primary segments of flagellum without aesthetascs; accessory flagellum 2-segmented. Antenna II with small calceoli in males. Upper lip rounded apically, margin not incised. Mandible with well-developed incisor process and lacinia mobilis and underlying row of spines; molar process triturative; palp 3-segmented. Maxilla I: inner plate with 2–4 long plumose setae apically; outer plate with seven robust serrate spines apically; palp 2-segmented, with short setae and spines apically. Maxilla II: inner plate oval, broader than outer plate, with oblique row of long plumose setae along inner margin; both plates with numerous setae apically. Maxilliped: inner plate with numerous spines and stiff-like setae apically; outer plate with short stiff-like setae on apex and along inner margin; palp 4- segmented. Lower lip with well-developed outer lobes; inner lobes small; lateral processes rather short, usually narrowly rounded distally. Gnathopods I–II robust, unequal in size and dissimilar shape (GnI smaller than GnII); palm of GnI mostly trapezoidal in shape, while palm of GnII close to rectangular-like form; palmar margin in both gnathopods with double row of typically distally notched spines. Pereopods III–IV mostly subequal, pereopod V shorter than pereiopods VI and VII. Coxal gills on pereopods II–VI moderately small, pedicellate, oblong. Posterior corners of epimeral plates I–II sharp, posterior margins with few short setae, ventral margins with few spines, differing in size. Pleopods biramous, subequal in length, with two coupling hooks in retinacula. Uropods I–II biramous, rami and peduncles armed with strong simple spines; uropod I greatly with equal rami; uropod II with equal rami, about as long as length of peduncle; uropod III uniramous, with short non-segmented ramus. Telson rectangular in shape, distal margin with deep Vshaped distal notch, reaching almost 1/2 of length of telson.

DIFFERENTIAL DIAGNOSIS. The genus Diasynurella is well distinguished from all other Palearctic genera of the family Crangonyctidae by the following features: 1) free urosomal segment I (fused in Pontonyx , Synurella and Lyurella ); 2) fused urosomal segments II and III with distinct sutures (vs. free urosomal segments in Amurocrangonyx , Crangonyx , Uralocrangonyx and Palearcticarellus ; completely fused urosomal segments without suture in Synurella ); 3) well developed inner lobes of labium (vs. almost completely reduced in Eosynurella ); 4) subquadrate propodus of gnathopods I (vs. oval propodus of pereopod I in Amurocrangonyx , Crangonyx , Uralocrangonyx and Palearcticarellus ); 5) elongated propodus of gnathopod II (mostly oval in Pontonyx , Amurocrangonyx , Crangonyx , Uralocrangonyx and Palearcticarellus ); 6) simple endopodite of uropod I (vs. paddle-like endopodite of uropod I in Volgonyx ); 7) well-developed two-segmented uropod III (vs. rudimentary two-segmented uropod III in Pontonyx and Synurella ; and mostly reduced unsegmented uropod III in Lyurella ); 8) the absence of an additional terminal knob on peduncle of uropod III (vs. present in Pontonyx ); 9) with single additional spine-like setae on dactyli of pereopods III–VII (vs. Amurocrangonyx , Eosynurella and Lyurella ); 10) two coupling hooks in retinacules of pleopods (vs. more than two hooks in Amurocrangonyx , Synurella , Palearcticarellus , Crangonyx , Uralocrangonyx and Volgonyx ).

ECOLOGICAL REMARKS. All species of the genus are characterized by number of the following common ecological features: 1) mature adults have very small body sizes (3.0– 4.5 mm of total body length); 2) females of all species carry only one– two eggs, which are very large and occupy the entire volume of marsupial cavity; and 3) it is obvious that these crustaceans are not able to spread beyond water resources of spring or spring/cave system, since all currently known species are found only in single spring or cave watercourse.