Gaetanus Giesbrecht, 1888
Taxonomic description:
Female. Total length 1.70-9.20 mm. Cephalothorax 3-5 times longer than abdomen. Rostrum present, one-pointed, not large, often with little excavation on the top. Frontal spine of different shape and size present or absent. Cephalon and Th1 fused (sometimes line of fusion visible). Th4-Th5 fused. Posterior Th5 corners symmetrical, rounded, with spines of different size and shape, in one species absent (G. inermis ). Genital segment symmetrical. Posterior borders of Abd1-3 often with rows of minute spinules. Caudal rami slightly longer than wide, or they are equal. Length of A1 varies from slightly longer than cephalothorax to longer than body, or even twice as long as body. Re A2 1.1-1.5 times longer than Ri A2. Re1 A2 without setae or with 1 seta. Re2 A2 with 1-3 setae, Re3-Re6 with 1 seta each, Re7 with 3 terminal setae and 1 medial; Ri1 A2 with 1-2 setae; Ri2 A2 usually with 7 terminal (rare 6) setae and 1 posterior on external lobe and 8(7) setae on internal lobe. Md palp base with 1-2 setae, Ri1 Md with 1-2, Ri2 Md with 9 terminal setae, often there are also 1-2 small, thin posterior setae. Mx1 gnathobase with 9 claw-like spines and 1 small terminal seta and 4 setae on posterior surface of the lobe; second lobe with 4-5, third with 4 setae, protopodite near Ri base with 5, Ri with 14-15 setae, Re with 11 and external lobe with 9 setae. Mx2 fourth and fifth endites with one of setae thickened and stronger sclerotized. Mxp protopodite with lateral plate of different size and configuration (or it is absent); it bears (counting from proximal to distal end of segment) groups of 2, 3 and 3 setae (at the base of the latter there is a small appendage, resembling a teat), usually there is 1 seta at the base of the segment in its proximal part; Ri1 Mxp with 3 setae distally. Re P1 2-3-segmented, with 2-3 external spines. Ri P2 2-segmented, rarely the division between segments incomplete. Other P2-P4 rami 3-segmented, P4 coxopodite with group of 11-35 spines, arranged as bush.
Male. Total length 1.86-7.00 mm. Cephalothorax about 3 times longer than abdomen. Rostrum present. Frontal spine, if present, smaller than in females. Spines on posterior Th5 corners rudimentary in comparison with that in females, rarely absent. Number of A1 segments less than in female, they are usually supplied with aesthetascs. Setation of oral parts reduced in comparison with that in females. Lateral plate on Mxp protopodite always absent. Number of spines on Re P1 usually less than in female. P2-P4 like in female, but spines on P4 coxopodite absent. P5 asymmetrical, biramous, Ri one-segmented, left Re P5 3-segmented, right 2-segmented. P5 of simple structure.
Remarks. The present program follows Park (1975b), who united Gaetanus Giesbrecht, 1888 and Gaidius Giesbrecht, 1895 and use the name Gaetanus due to the rule of priority.
Type species: Gaetanus miles Giesbrecht, 1888, by subsequent designation (Brodsky, 1950).
The genus Gaetanus includes 24 species.
Gaetanus antarcticus Wolfenden, 1905
Gaetanus armiger Giesbrecht, 1888
Gaetanus brachyurus Sars, 1907
Gaetanus brevicaudatus (Sars, 1907) (male unknown)
Gaetanus brevicornis Esterly, 1906
Gaetanus brevirostris (Brodsky, 1950)
Gaetanus brevispinus (Sars, 1900)
Gaetanus curvicornis Sars, 1905 (male unknown)
Gaetanus inermis Sars, 1905 (male unknown)
Gaetanus kruppii Giesbrecht, 1903
Gaetanus latifrons Sars, 1905
Gaetanus miles Giesbrecht, 1888
Gaetanus minispinus Tanaka, 1969 (male unknown)
Gaetanus minor Farran, 1905 (male unknown)
Gaetanus minutus (Sars, 1907)
Gaetanus paracurvicornis Brodsky, 1950 (male unknown)
Gaetanus pileatus Farran, 1903
Gaetanus pseudolatifrons Markhaseva 1996
Gaetanus pungens (Giesbrecht, 1895)
Gaetanus robustus Sars, 1905
Gaetanus rubellus Markhaseva 1996
Gaetanus secundus Esterly, 1911
Gaetanus simplex Brodsky, 1950
Gaetanus tenuispinus (Sars, 1900)