Azygokeras Koeller and Littlepage, 1976
Taxonomic description:
Female. (Description after Koeller and Littlepage (1976) with modifications). Total length 2.58-2.87 mm. Cephalothorax about 3.5 times longer than abdomen. Cephalon and Th1 fused, Th4-Th5 separated. Rostrum and crest absent. Th5 posterior corners elongated into points not separated from Th5, covering the first third of genital segment. Th5 and Abd1 symmetrical. Abd1-Abd3 covered with small denticles along posterior border. A1 24-segmented, with numerous setae, annulated in their distal part. Re and Ri A2 equal in length; coxopodite with 2 setae (instead of 1 in remaining aetideid genera); basipodite with 2 setae; Ri1 A2 with 2 setae in distal part of segment, Ri2 A2 with 14 setae (8 at internal and 6 at external lobe); Re1 A2 lacking setae, Re2 A2 with 3 setae, Re3-Re6 A2 supplied with 1 seta each, Re7 A2 with 3 terminal setae. Md palp base with 3 setae, Ri1 Md with 2, Ri2 Md with 9 terminal and 1 posterior setae; Re Md typical of Aetideidae, it is more than 1.5 times longer than Ri. Mx1 gnathobase with 9 claw-like terminal (2 thinner) and 2 small setae on the posterior surface of segment, surface supplied with minute spinules; second and third internal lobes with 4 setae each, at protopodite near the Ri base 5 setae; Ri with 15, Re with 11 setae, external lobe bearing 7 setae. Mx2 typical of Aetideidae. Protopodite Mxp strong, twice as long as wide, with groups of 1 proximal, 3 medial and 3 distal setae; Ri1 Mxp with 3 setae removed from medial part of segment to distal. P1 with 3-segmented Re and one-segmented Ri; all Re segments with external spine each, each spine nearly reaching the base of next spine. Segmentation of P3-P4 typical of Aetideidae; rami 3-segmented. Posterior surfaces of Ri P2-P4 with minute spinules. P2 and P3 with groups of spinules on posterior and anterior surfaces also externally at coxopodite and on posterior surface of basipodite near the base of Re.
Male. Total length 2.08-2.10 mm. Cephalothorax about 3 times longer than abdomen. Rostrum and crest absent. Segmentation of cephalothorax as in female, Th5 more reduced, but posterior corners of Th5 triangular shape, reaching posterior border of Abd1. Left A1 22-segmented, right 21-segmented, nearly all segments supplied with aesthetascs. Right A1 geniculated, last 6 segments in comparison with others enlarged, these segments are curled in circle, and their setae transformed in robust spines. A2 similar to that in female, but Ri2 A2 without setae, setae at Re1 and Re2 A2 reduced. Md without gnathobase, base of mandibular palp lacking setae, Ri1 with 1, Ri2 Md with 9 setae. Mx1 and Mx2 rudimental in comparison with that in female. Mxp more slender than in female, protopodite lacking setae, Ri1 Mxp with 1 medial seta, P1 similar to that in female, at external margin of basipodite there are long thin spinules, P2-P4 as in female. P5 biramous, Ri one-segmented, Re 3-segmented, legs of simple structure.
Type species: Azygokeras columbiae Koeller and Littlepage, 1976, by original designation.
Remarks. This genus is unique in Aetideidae because of geniculated right A1 in male.