Chiridius Giesbrecht, 1892
Taxonomic description:
Female. Total length 1.59-4.60 mm. Cephalothorax 2.00-4.00 times longer than abdomen. Rostrum absent. Cephalon and Th1, as well as Th4-Th5 fused. Posterior Th5 corners prolonged into points not separated from segment, symmetrical, their length may cover first third of genital segment, or they may reach middle, or end of second third of length of the genital segment (dorsal view). Points are directed almost straight to the posterior end of the body, sometimes slightly divergent (dorsal view). Distal part of spermathecae of oval or rounded shape, from which thin duct is deviating (in Ch. obtusifrons distal part of spermathecae not much wider than the duct). Posterior borders of Abd1-3 with minute spinules. Genital segment symmetrical. Length and width of genital segment are nearly the same, sometimes length is slightly more than width, 1.3-1.6 times longer than Abd2. Length of caudal rami about 1.5 times more than width. A1 24-segmented, as long as cephalothorax, or may reach the middle of the genital segment, or Abd2, or even the posterior border of Abd3 (Ch. mexicanus ). Re A2 1.5-2.0 times longer than Ri; coxopodite A2 with 1, basipodite A2 with 2 setae, Ri1 A2 with 2 setae, Ri2 A2 with 8 (rarely 7) setae (of which usually 4-5 longer and stronger) on internal lobe, and 6 long setae and often 1 short posterior seta on external lobe. Re1 A2 lacking setae, Re2 A2 with 2 (1 medial and 1 distal) setae, Re3-Re6 each with long, strong seta, Re7 A2 with 1 medial short and 3 terminal setae. Md palp base with 2, Ri1 Md with 2 setae, Ri2 Md with 8-9 terminal (sometimes 7 terminal and 1 dorsal: Ch. polaris , Ch. pacificus ) setae (usually 1-3 of them thinner and shorter). Re Md nearly 1.5-2.0 times longer than Ri. Mx1 gnathobase with 9 claw-like terminal, 1 anterior and 4 setae on posterior surface, 5 setae are on the second internal lobe, 4 on third internal lobe, 4 setae on protopodite near Ri base (of which 1 strong and long, other short and thin), Ri with 11-13 setae, Re with 8 or 10 setae; on external lobe 7 (rarely 6) long and 2 short setae. Mx2 typical of the family: 1 seta (of 3) on fourth and fifth endites transformed into claw-like. Ri1 Mxp 1.2-1.5 times longer than protopodite, protopodite with 3 groups of 2, 3 and 3 setae (looking from proximal to distal part of the segment), beside these, there is 1 more seta near segment base; on the lateral surface of Ri2 Mxp sometimes semicircular row of spinules is visible (Ch. polaris ). Re P1 3-segmented, each segment supplied with external spine; on anterior surface of Re2 P1 often a group of spinules is present. Ri P2 1- 2-segmented, Re P2 2-3-segmented, Ri P2 not reaching, or reaching the border between Re2-Re3 P2, sometimes even exceeding it (Ch. poppei ). Re3 P2 edge between second and third external spines sometimes with bulge (Ch. molestus ). P3 and P4 rami clearly, rarely unclearly 3-segmented. External spines of Re3 P4 often significantly shorter and thinner than that on P3.
Male. Total length 1.50-3.80 mm. Cephalothorax 2.5-3.3 times longer than abdomen. Rostrum absent. Cephalon and Th1, as well as Th4-Th5 fused, line of fusion is weakly visible dorsally. Posterior Th5 corners prolonged into points, not separated from the segment and reaching the midlength of genital segment, or exceeding its posterior border. Posterior border of Abd2-4 with minute spinules. Abd2 1.4-1.9 times longer than genital segment. A1 23-segmented, may be shorter or as long as cephalothorax, reach the end of the genital segment, or posterior border of Abd2. Re A2 1.3-1.6 times longer than Ri. Ri2 A2 with 11-12 setae, coxopodite with 1 seta, basipodite with 1-2 setae, Ri1 A2 with 1 seta, less in size than in female. Md palp base with 1 seta, or it is absent. Setae (usually there is one seta) on Ri1 Md shorter and thinner than in female; Ri2 Md with 9 (Tanaka, 1957a noted for Ch. molestus 8 setae). Mx1 with 8-9 setae on Ri, 9 on Re, on gnathobase and second internal lobe setae absent. Mxp with protopodite 1.06-1.40 times longer than Ri1 Mxp, that usually bears 3 medial setae, but in Ch. molestus only 1 medial seta present. Segmentation and setation of P1 is the same as in female, but first and second external Re spines, as a rule, shorter. P2 with 2-segmented Ri, sometimes segmentation indistinct (Ch. poppei ), the line of separation between segments is better visible than in female. In other species Ri P2 just reaching (or not) the border between Re2 and Re3 P2, only in Ch. poppei it exceeds the border of Re2-Re3 P2. First and second external spines on Re3 usually as in female of corresponding species. P3, P4 with 3-segmented rami (in Ch. obtusifrons segmentation in P4 indistinct). P5 uniramous, only in Ch. pacificus rudimentary Ri present in both rami; if uniramous, usually right leg 4-segmented longer than 5-segmented left (in Ch. poppei they are of about the same length). P5 in Ch. longispinus is about half as long as P4, in other species they are longer.
Type species: Chiridius poppei Giesbrecht, 1892, by monotypy.
The genus Chiridius includes 8 species, all of them except Ch. mexicanus Park, 1975 are described below. Ch. subantarcticus Park, 1978 is herein considered to be synonym of Ch. polaris Wolfenden.
Chiridius gracilis Farran, 1908
Chiridius longispinus Tanaka, 1957 (female unknown)
Chiridius molestus Tanaka, 1957
Chiridius obtusifrons Sars, 1902
Chiridius pacificus Brodsky, 1950
Chiridius polaris Wolfenden, 1911
Chiridius poppei Giesbrecht, 1892