List species and varieties by family
Mesaiokeratidae Matthews, 1961 ( Clausocalanoidea )
(1) Mesaiokeras Matthews, 1961
Rem.: Hyperbenthic forms.
On the occasion of the description of this new genus, Matthews discusses the validity of two sections Amphascandria and Isokerandria.
The family Mesaiokeratidae shows characters that are similar to those of the Scolecitrichidae and the Diaixidae.
Type: Mesaiokeras nanseni Matthews,1961. Total: 9 spp.

Diagnosis from Bradford-Grieve (1994, p.95) :
- As for the family definition.
- Small rostral filaments present.
- Setation on the caudal rami may be asymmetrical.
- Last endopodal segment of A2 elongate, with no distinct lobe.
- Endopod of P1 with a straight outer margin and exopod usually with a reduced number of spines on the outer margin.
- Left P5 male very long, uniramous and 5-segmented; right leg short, not extending beyond exopodal segment 1 of the left leg.

Key to species after Boxshall & Halsey (2004, p.144) (not included : M. hurei Krsinic, 2003, and M. spitsbergensis Schulz & Kwasniewski, 2004) :
1 – Female A1 24-segmented (apical segment double XXVII-XXVIII) ; 1st exopodal segment of P1 with outer spine ……… M. heptneri.
1’ – Female A1 23-segmented (apical segment triple XXVI-XXVIII) ; 1st exopodal segment of P1 without outer spine …….. 2.
2 – 2nd exopodal segment of P1 with outer spine ; penultimate segment of male left P5 with row of large spinules along margin …… M. mikhailini.
2’ – 2nd exopodal segment of P1 without outer spine ; penultimate segment of male P5 without row of large spinules along margin …… 3.
3 – Male left P5 with truncated distal margin of terminal segment armed with at least 2 strong spines plus a rounded setal element subapically ……. 4.
3’ – Male left P5 with terminal segment tapering to acute point ; segment armed with 1 or 2 setal elements …… 5.
4 – Left caudal ramus of female with long naked seta positioned proximally near inner margin and directed laterally ; 4th and 5th pedigerous somites fused ; distal segment of male left P5 armed with 1 strong spine and 1 rounded element …… M. nanseni.
4’ – Left caudal ramus of female without such a modified seta ; 4th and 5th pedigerous somites separate ; distal segment of male left P5 armed with 2 strong spines ……M. semiplenus.
5 – Terminal segment of male left P5 armed with 2 strong spines at mid-length ; penultimate segment lacking distal spinous process …… M. kaufmanni.
5’ – Terminal segment of male left P5 with 1 subapical spine and 1 proximal spine ; penultimate segment lacking distal spinous process …… M. marocanus.
5’’ – Terminal segment of male left P5 with 2 closely adpressed spines subapically ; penultimate segment produced into distal spinous process ….. M. tantillus.

[1] Mesaiokeras heptneri  Andronov, 1973   (F,M)    [Figs]

[2] Mesaiokeras hurei  Krsinic, 2003   (F,M)    [Figs]

[3] Mesaiokeras kaufmanni  Fosshagen, 1978   (M)    [Figs]

[4] Mesaiokeras marocanus  Andronov, 1995   (M)    [Figs]

[5] Mesaiokeras mikhailini  Andronov, 1995   (M)    [Figs]

[6] Mesaiokeras nanseni  Matthews, 1961   (F,M)    [Figs]

[7] Mesaiokeras semiplenus  Andronov, 1973   (F,M)    [Figs]

[8] Mesaiokeras spitsbergensis  Schulz & Kwasniewski, 2004   (F,M)    [Figs]

[9] Mesaiokeras tantillus  Andronov, 1973   (F,M)    [Figs]

 Any use of this site for a publication will be mentioned with the following reference :

Razouls C., Desreumaux N., Kouwenberg J. and de Bovée F., 2005-2022. - Biodiversity of Marine Planktonic Copepods (morphology, geographical distribution and biological data). Sorbonne University, CNRS. Available at http://copepodes.obs-banyuls.fr/en [Accessed November 28, 2022]

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