type: Calanoides patagoniensis Brady,1883, not C. carinatus Kröyer,1849.
6 spp.

Redefinition from Bradford & Jillett (1974, p.9) :
- Cephalon and 1st thoracic segment partly fused.
- A1 male with segments 3 to 5 fused, though weak lines of separation are usually apparent.
- Mx2: 1st lobe with 5 setae.
- Mxp with fewer setae than in other calanids: terminal 5 segments with 4, 3, 2, 3 and 4 setae respectively.
- Male mouthparts reduced.
- Swimming legs without modification or ornamentation.
- 1st basipod (= coxopodite) of P5 with naked inner border in both sexes. Female P5 endopod with 6 setae. Male P5 endopods often reduced and unsegmented but never with more than 6 setae.
- Among the species of this genus, C. acutus has the least modified male mouthparts and C. philippinensis the most modified mouthparts.

type: Monoculus finmarchicus Gunnerus, 1770. 14 spp.

Redefinition after Bradford-Grieve (1994, p.299) :
- Cephalon and 1st thoracic segment partly fused.
- A1 male with segments 3 to 5 fused in some cases.
- Mouthparts the same in both sexes;
- Mx2 with 5 or 6 setae on the 1st inner lobe.
- Swimming legs without modification or ornamentation.
- P5 with a toothed inner border on the 1st basipods (= coxopodite) in both sexes.
- Female P5 endopod with 8 setae;
- Male P5 with both rami 3-segmented, both endopods with 8 setae.

Marshall & Orr (1972, p.159-166 & litt.) underline the role of this genus in the food web, particularly as source of food for various planktonic forms and fishes, euphausids, whales, basking shark (Cetorhinus maximus), and even sea birds. In Antarctic, the chief food during the polar summer of Euphausia superba are copepods. In the Arctic other euphausids ( Thysanoesssa, Meganyctiphanes) or Calanus or a mixture. On the Norwegian coast Balaenopterus borealis (Sei whale) lives chiefly on copepods, especially Calanus finmarchicus (Hjort & Ruud, 1929; Hjort, 1933). For whales F.C Fraser (pers. comm.) has calculated thet the mouth of a right whale has a capacity of 1.5 m³, and that the corresponding figure for a rorqual is 2-3 times as much. The basking shark can filtered 2000 m³ per hour through the gill rakers.

type: Calanus pauper Giesbrecht, 1888. 1 sp.

Redefinition after Bradford & Jillett (1974, p.10) :
- Cephalon and 1st thoracic segment fused.
- Mouthparts same in both sexes;
- Mx2 with 4 setae on the 1st inner lobe.
- P1: 1st basipod (= coxopodite) anterior margin terminates in a well defined projection; 2nd basiopod with distal seta on anterior surface modified into a proximally thickened spine.
- P2 to P4 without modification or ornamentation.
- P5 with the inner border of the 1st basipod (= coxopodite) naked in both sexes.
- Female P5 endopod with 7 setae. Male P5 with both rami 3-segmented, hardly modified on right; left endopod with only 2 terminal setae.
- For the authors, this genus occupies an intermediate position between those genera with a dentate inner border to the P5 coxopodite and also with similar mouthparts in both sexes, and those genera with a naked inner border to the P5 coxopodite and reduced male mouthparts.

type: Undina darwini Lubbock,1860. Total: 2 spp.

Definition from Bradford & Jillett (1974, p.12) :
- Cephalon and 1st thoracic segment fused.
- A1 of male with segments 3 to 5 fused.
- Postero-lateral corners of cephalothorax pointed in female.
- Mouthparts similar in both sexes.
- 1st inner lobe of Mx2 with 5 setae.
- Basal segments of the swimming legs ornamented with spines; these spines on the anterior surface of 1st basisipods of P1, and P3 to P5 in the famale; and P1, P3 and P4 in the male; these spines also on the posterior surface of 2nd basipods of P2 and P3.
- P5 of both sexes with teeth on the inner borders of the 1st basipods.
- Female P5 endopods with 7 setae.
- Male P5 with 1-segmented, rudimentary left endopod; left exopod highly modified compared with Calanus type: 1st exopodal segment normal; 2nd segment external spine very elongate with inner peg-like projection: 3rd segment elongate and complicated. Right leg not modified.

For Brodsky (1980: pers. comm.) the creation of this genus appears not well guaranteed. Type : Calanus tenuicornis Dana,1849. Total: 2 spp.

Definition from Bradford & Jillett (1974, p.12) :
- Cephalon and 1st thoracic segment separate.
- A1 with segments 8 and 9 fused in female; in male segments 3 to 5, 7 and 8, and 9 and 10, fused.
- Male mouthparts reduced.
- Mx2 with 6 setae on the 1st inner lobe.
- Swimming legs P1 to P4 without modification or ornamentation.
- 1st basipod (coxopodite) of P5 with a smooth inner border in both sexes. P5 endopod of female with 7 setae. P5 male with both rami 3-segmented, endopods with 7 setae.
- For the authors, this genus is intermediate between Neocalanus and Calanoides.

type: Cetochilus minor Claus,1863. Total: 2 spp.

Definition after Bradford-Grieve (1994, p.39) :
- Cephalon and pedigerous segment 1 fused in both female and male. Otherwise very similar to Calanus.
- Right and left spermathecae fused on female genital segment.
- Male A1 with segments 1-2, 3-5, 24-25 fused.
- Male right P5 like other swimming legs, i.e, with setae on the inner border of the exopod, left endopod without setae, left exopod with outer edge spines greatly elongated.
- For the authors, it was incorrect in treating Nannocalanus as a synonym of Calanus (Bradford & Jillett, 1974, p.9) because N. minor would have been the only male in Calanus which had the exopod of the right P5 like the other swimming legs. That is, it has inner edge setae. Also the male P5 has a reduced number of setae or spines on the endopods and left exopod segment 3 compared with Calanus. The female of N. minor would have been the only female with the right and left spermathecae apparently fused (Brodsky, 1972). Brodsky (1972) considers Nannocalanus to be a junior synonym of Canthocalanus and erroneously assigns N. minor as its type species. This conclussion cannot be supported.

type: Calanus gracilis Dana,1849. Total: 6 spp.

Redefinition after Bradford & Jillett (1974, p.10) :
- Cephalon and 1st thoracic segment fused or separate.
- A1 male may have segments 24 and 25 fused.
- Male, and sometimes female, mouthparts reduced; Mx2 with 6 setae on 1st inner lobe.
- P2, in both sexes, with a recurved spine at the outer distal border of the 1st exopodal segment. 1st basipod (= coxopodite) of P5 with inner border naked in both sexes.
- Male P5 with both rami 3-segmented; left leg modified, endopod usually with 8 setae; right leg unmodified, or with inner edge setae of exopod absent.
- For the authors, N. gracilis and N. robustior are very closely related, both having the cephalon and 1st thoracic segment fused; the A1 male with segment 25 very small and fused to segment 24. N. plumchrus has the greatest mouthpart reduction in the both sexes.

After Ohtsuka & Nishida (2019, p.575), the divergence and colonization of Neocalanus are deduced in accord with Cenozoic events (< - 55 million years) (Machida & al., 2006; Ohtsuka & al., 2009). The taxa showing antitropical distributions are characterized by adaptationj to seasonal phytoplankton blpoom and by ontogenetic vertical migration, consistent with their origin in the Oligocene (- 34-23 million years). In addition, The existence of three Northern Hemisphere species suggests that speciation could have occurred in marginal seas after the Miocene (- 23-5.3 million years)

Type: Undina vulgaris Dana,1849. Total: 1 sp.

Redefinition after Bradford & Jillett (1974, p.11) :
- cephalon and 1st thoracic segment fused.
Female thoracic corners extend postero-laterally into 1 or 2 points.
- Mouthparts similar in both sexes; Mx2 1st inner lobe with 6 setae.
- P2 with invaginate outer proximal border of the 2nd exopodal segment in both sexes.
- P5 1st basipod (= coxopodite) with inner border naked in both sexes; Female P5 endopod with 7 setae; those on the 1st and 2nd segments spine-like. Male left P5 hihhly modified; outer edge spines of 1st and 2nd exopodal segments very elongate and the 3rd segment very modified; endopod absent. Male right P5 with both rami 3-segmented, endopod with reduced setation, 2nd exopodal segment with outer distal border elongate extending as far as the 1st outer spuine of segment 3.
- The authors have removed U; darwini Lubbock,1860 and U. caroli Giesbrecht,1888 from this genus as they both differ from Undinula vulgaris as follows: the inner borders of the basipod of P5 are toothed; P5 male though superficially similar, are modified in a completely different manner; the outer margins of the 2nd exopods of P2 are not invaginate; and the setae on the two basal endopodal segments of the female P5 are not thickened and spine-like.