Species Card of Copepod
Calanoida ( Order )
    Clausocalanoidea ( Superfamily )
        Mesaiokeratidae ( Family )
            Mesaiokeras ( Genus )
Mesaiokeras spitsbergensis  Schulz & Kwasniewski, 2004   (F,M)
Schulz & Kwasniewski, 2004 (p.145, figs.F,M)
Species Mesaiokeras spitsbergensis - Plate 1 of morphological figuresissued from : K. Schulz & S. Kwasniewski in Sarsia, 2004, 89. [p.146, Fig.2].
Female: A, habitus (lateral right side); B, idem (dorsal); C, rostrum (anteroventral); D, idem (lateral); E, genital segment (double somite) (lateral right side); F, idem (ventral); G, Anal somite and caudal rami (dorsal); H, caudal setae of left ramus (dorsal); I, caudal rami (ventral); K, A1 (segments I-XV); L, A1 (segments XVI-XXVIII.
Scale lines 0.05 mm.

Nota : A1 symmetrical, 24-segmented and extending to posterior margin of 2nd pedigerous somite ; fusions involving ancestral segments II-IV, X-XI, and XXVII-XXVIII, with articulation between segments III and IV incompletely expressed.
Genital double-somite with a group of spinules on both left and right sides at midlength ; common operculum widely rounded posteriorly ; left and right seminal receptacles small, forming dorsal short lobes. Posterior margin of genital double-somite to 3rd urosomal somite bearing hyaline frill.
Caudal rami about as long as wide, slightly asymmetrical along left and right medial margins, armed with 5 setae and foliaceous spinules on dorsal and lateral margins ; setae III-VI plumose and implanted distally ; seta VII subdistally along medial margin, left one distinctly stronger, naked and implanted anterior to short right plumose counterpart.

Species Mesaiokeras spitsbergensis - Plate 2 of morphological figuresissued from : K. Schulz & S. Kwasniewski in Sarsia, 2004, 89. [p.148, Fig.3].
Female: A, A2; B, Md (coxa); C, Md (palp); D, Mx2; E, Mxp; F, P1; G, P2; H, P3; I, P4.
Scale lines 0.05 mm.

Nota :
A2 : Coxa and basis almost fused ; coxa with row of long setules and inner distal seta ; basis with 2 distal setae on inner margin. Endopod 2-segmented. Exopod 7-segmented.
Mx2 : slender, comprising separate praecoxa and coxa, basis mostly incorporated into coxa, and 4-segmented endopod. 1st praecoxal endite with 3 long marginal and 2 submarginal setae, proximal one distinctly smaller ; 2nd praecoxal endite and both coxal endites armed with 3 setae each ; basal endite with 4 unequal setae, one small and slender. Endopod short, with setal formula 1, 2, 1, 1.

Species Mesaiokeras spitsbergensis - Plate 3 of morphological figuresissued from : K. Schulz & S. Kwasniewski in Sarsia, 2004, 89. [p.149, Fig.4].
Female: A, Mx1; B, P5.
Nota :
Mx1 : praecoxal arthrite with 9 marginal, 1 short anterior and 4 posterior setae ; coxal epipodite produced bearing 9 setae ; coxal endite with 3 setae ; 1st and 2nd basal endites carrying 2 and 4 setae ; 1st endopod segment almost fused to basis, with 5 setae ; 2nd segment with 5 setae ; exopod bearing 8 setae.
P5: slightly asymmetrical, uniramous, 3-segmented, with right ramus longer than left counterpart; both coxae fused with intercoxal sclerite to form common base; coxa and basis ornamented with spinules on posterodistal surface, few spinules implanted anteromarginally; terminal segment (exopod) bifurcate, with outer spiniform process (about 60% length of segment), both processes sparsely ornamented with strong spinules.

Male: C, habitus (dorsal); E, rostrum (ventral view); F, P5; G, right ramus and left 1st segment; H, distal two segments of left P5.
Scale lines 0.05 mm.
Nota: Posterolateral margins of thorax asymmetrical. Rostral filaments wanting. P5 uniramous, strongly asymmetrical ; both coxae completely fused. Right ramus 3-segmented ; 2nd segment ornamented with patch of spinules at outer distal corner. Left ramus 5-segmented comprising coxa, basis and 3-segmented exopod, very elongate.
Urosome 5-segmented ; genital somite with gonopore on left side.
Caudal rami with asymmetrical inner margins, bearing small, plumose seta VII implanted more anteriorly on left than on right ramus.

Species Mesaiokeras spitsbergensis - Plate 4 of morphological figuresissued from : K. Schulz & S. Kwasniewski in Sarsia, 2004, 89. [p.150, Fig.5].
Male: A, anal somite and caudal rami (dorsal); B, A1 (segments I-XVI); C, idem (segments XVII-XXVIII); D, Mx1; E, P4 (posterior); F, endopod of P4 (anterior).
Scale lines 0.05 mm.

Nota :
A1 symmetrical, 24-segmented, extending to end of 2nd pedigerous somite ; fusions as in female, but ancestral segments II-IV completely fused ; armature differing from female.

Compl. Ref.:
Hop & al., 2006 (p.182, Table 4)
NZ: 1

Distribution map of Mesaiokeras spitsbergensis by geographical zones
Arctic: Spitsbergen Is. (Kongsfjorden)
N: 2
(886) F: 0,88-1,05; M: 0,94;1,01; {F: 0,88-1,05; M: 0,94-1,01}
Rem.: hyperbenthic (depths ± 360 m).
Last update : 17/01/2015
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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 January 18, 2022]

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