Giesbrecht, 1892
Females
Pd1 and Ce usually fused, sometimes separate, Pd4 and 5 usually fused. R usually with 2 filaments, two-pointed, or absent. Posterior corners of Pr usually symmetrical, rounded, sometimes extended into triangular lobes (Farrania). Gns usually symmetrical. A1 generally with segments 8-9 fused and sometimes with segments 1-2 and 24-25 fused; extremely long setae absent. A2 Exp 6-segmented (Clausocalanus, Ctenocalanus, Drepanopus, Microcalanus) or 7-segmented (Farrania); Exp1 with 1 or 2 setae, or setae are absent; Exp2 with 2 medial setae, or setae are absent. Coxa with 1 seta, Basis with 2 setae; Enp1 with 2 setae. Mdp Basis with 4 setae; Enp1 with 4 setae and Enp2 with 9 terminal and 1-2 appendicular setae (Clausocalanus, Drepanopus), or 5 (Farrania pacifica) setae. Mx1 Li1 with 9 terminal, 1 anterior and 4 posterior setae; Li2 with with 5 setae, Li3 with 4 setae, Li4 with 5 setae; Enp with up to 16 setae; Exp with 11 setae; Le1 with 9 setae (Clausocalanus). Mx2 Li1-Li5 with 3-5, 3, 3, 3 and 4 setae respectively; Li6 and terminal part of limb usually with 6 setae, or up to 7 setae. Mxp Coxa with 1 proximal setae, then with groups of 2, 3 and 3 setae from proximal to distal; Enp1-5 with 4, 4, 3, 4 and 4 setae respectively, Basis with inner proximal row of fine spinules (in Drepanopus setation is reduced). P1 Enp with external lobe, or may be absent (Microcalanus, Drepanopus bungei). In Drepanopus P2 Enp may be 1-segmented and Enp of P4 not completely 3-segmented (D. bungei). Posterodistal border of Basis of P2 and 3 may be ornamented with spines, Enp of P2-4 usually narrow. Surfaces of legs with or without spinules.
Spine and seta formula: Spine and seta Clausocalanidae.
P5 absent (Microcalanus, Pseudocalanus), or present. If present, uniramous on both sides, symmetrical, 3-segmented terminally produced into short bifid, pointed processes (Clausocalanus); or with 2-3 terminal spines (Farrania); or consisting of very small appendage, developed only on left and of 2-4 segments (Ctenocalanus); or symmetrical, 2-segmented with large curved terminal spine, pectinated along its distal outer half (Drepanopus).
Males
A1 with segments 1-2 and 8-10 always fused; several other segments may be also fused. A2, Md, Mx1 and Mx2 usually reduced in size and setation compared with female. P1-P4 as in female, although there may be some sexual dimorphism in the proportions of legs and spinulation. P5 present on both sides, but of unequal length, uniramous; longer leg nearly always on left, 5-segmented, shorter leg 1-3 segmented, less than half length of Coxa of other leg (Clausocalanus, Ctenocalanus), or longer (Microcalanus); or both legs of similar length (Pseudocalanus), sometimes even with rudimentary Enp (some species of Drepanopus, Farrania).
There are at least six genera in the family; of which the four marked (*) below occur in the South Atlantic:
Genus Clausocalanus Giesbrecht, 1888 *
Genus Ctenocalanus Giesbrecht, 1888 *
Genus Drepanopus Brady, 1883 *
Genus Farrania Sars, 1920 *
Genus Microcalanus Sars, 1901
Genus Pseudocalanus Boeck, 1873
Genus Spicipes Grice and Hülsemann, 1965
The genus Clausocalanus was revised by Frost and Fleminger (1968).