Undeuchaeta Giesbrecht, 1888
Taxonomic description:
Female. Total length 3.00-6.60 mm. Cephalothorax 3-4 times longer than abdomen. Crest present, or absent. Rostrum present, one-pointed. Cephalon and Th1 unclearly separated, or fused; Th4-Th5 fused. Th5 posterior corners prolonged into obtuse triangular, or triangular lobes, sometimes asymmetrical and one of them may be rounded. Genital segment asymmetrical: small projection (U. incisa , U. major ), or spine (U. plumosa , U. bispinosa ) may be present on the right. Genital segment usually with spinules along posterior border, sometimes groups of minute hairs arranged in other parts of segment. A1 23-24-segmented, nearly as long as cephalothorax, or reaching Abd3. Re A2 nearly twice as long as Ri A2; Re1 A2 without setae, or with 1 very small reduced seta; Re2 A2 with 1 hardly visible distal seta (sometimes there are 2 small setae); Re3-Re6 with 1 long seta each, Re7 carries 1 medial and 3 terminal setae. Ri1 A2 with 2 distal setae, Ri2 A2 with 6 long posterior setae and 1 short on external and 8 (6 long, 2 short, or 7 long, 1 short) setae on internal lobe. Md palp base with 3 setae, Ri1 Md with 2 setae (in U. intermedia only 1 seta visible) and Ri2 Md with 9 terminal and 1 short posterior setae. Mx1 gnathobase with 9 claw-like setae and 1 thin terminal one, and also with 4 setae on posterior surface of Mx1 gnathobase; second internal lobe with 5, third with 3 setae, protopodite near Ri base with 5 setae, Ri with 14-15 setae, Re with 11, external lobe with 9 setae. Mx2 of typical structure, in claw-like transformed 1 seta on each fourth and fifth endites. Mxp protopodite 1.7-1.9 times shorter than Ri1 Mxp; Re3 Mxp nearly twice wider than each of neighbouring segments (Re2 and Re4); protopodite in its proximal part with 1 seta, and 3 groups of 2, 3 and 3 setae (from proximal to distal). Re P1 3-segmented, separation between Re1 and Re2 P1 unclear; Re1 without external spine, other Re P1 joints with spines. Ri P1, Ri P2 one-segmented, all other swimming leg's rami 3-segmented. Large spines on P4 coxopodites absent, rarely there are small spinules.
Male. Total length 2.85-5.58 mm. Cephalothorax about 3 times longer than abdomen. Cephalon and Th1, as well as Th4 and Th5 fused. Rostrum developed less than in females, also one-pointed. Crest, if present is small. Th5 posterior corners slightly asymmetrical, rounded. A1 22-23-segmented, reaching the end of cephalothorax, or the distal end of Abd3. Segmentation of A2 the same as in female, but setation reduced: coxopodite lacking setae, basipodite with 1 seta, Re1 A2 with 1 very small seta (or it is absent), Re2 A2 without seta, medial seta on Re7, if present very small, also on each external and internal lobes of Ri2 A2 there is 1 seta less than in female. Md palp base with 1 seta, Ri1 Md with 1, Ri2 Md with 9 terminal setae, posterior one is absent. Mx1 setation reduced, Re Mx1 with 10 setae. Mx2 and Mxp reduced. Park (1978) noted for U. incisa Mxp protopodite with 3 groups of 1, 2 and 3 setae (from proximal end of segment). Separation between Re1 and Re2 P1 more clear than in female, Re1 P1 without spine, external spine on Re2 shorter than in female. Ri P2 unclearly one-segmented, with traces of separation into 2 segments. All other swimming leg rami P1-P4 3-segmented. P5 powerful, biramous, usually not shorter, sometimes even longer than abdomen, coxopodites are fused, basipodites powerful, strongly sclerotized, left one longer than right by about one third of its length. Left and right Ri P5 one-segmented, left Re P5 3-segmented, apical end of Re3 P5 prolonged into stylet-like projection with spine-like top, distal part of Re2 P5 with tooth-like projection. Right Re P5 2-segmented.
Remarks . As U. major Giesbrecht, 1888 was designated as type species after subsequent indication (Brodsky, 1950; Park, 1978).
Type species: Undeuchaeta major Giesbrecht, 1888.
The genus Undeuchaeta includes 4 species. Following Vervoort (1957) I am inclined to consider U. bispinosa as junior synonym of U. intermedia.
Undeuchaeta incisa Esterly, 1911
Undeuchaeta intermedia A. Scott, 1909 (male unknown)
Undeuchaeta major Giesbrecht, 1888
Undeuchaeta plumosa (Lubbock, 1856)