Calanoida ( Order )
    Spinocalanoidea ( Superfamily )
Arctokonstantinidae Markhaseva & Kosobokova, 2001 ( Spinocalanoidea )
Ref.: Markhaseva & Kosobokova, 2001 (p.319); Markhaseva, 2008 (p.9, 12, 15); Markhaseva & Schulz, 2008 a (p.279, Table 1, Rem., p.287); Blanco-Bercial & al., 2011 (p.103, Table 1, Fig.2, 3, 4, Biol. mol, phylogeny); Laakmann & al., 2019 (p.330, fig. 2, 3, phylogenetic relationships)
Rem.: 5 G.: Arctokonstantinus, Caudacalanus, Foxtonia, Foxtosognus, Sognocalanus.

For Markhaseva & Kosobokova (2001, p.320) the family differs from the spinocalanids in the following apomorphies : 1- Mx2 is strongly transformed with distal endites attenuated into claw-like protrusions, setal equipment as follows : 1st lobe with 2 setae, 2nd lobe with 2 thick short spines plus 1 thin seta, 3rd lobe with 2 thick short spines, 4th and 5th lobe transformed into claw-like attenuations with 1 seta retained on each, distal part of limb with 4 setae. 2- Mxp syncoxa with 1 minute seta, basis with 2 setae located in the proximal part of the segment, endopod segment 1 (fused to basis) with 1 seta, endopod 2 with 2 setae, endopod 3-4 with 1 seta each, endopod 5 with 2 setae, and endopod 6 with 3 setae. 3- P1 exopod 1-segmented with 4 inner setae. 4- P2 endopod 1-segmented.


For Markhaseva & Schulz (2008, p.279) this family is not treated as a junior synonym of Spinocalanidae, because it is distinguished from the latter by the following apomorphies :
1- Mandibular basis bears less than 3 setae (vs. 3-4 setae in Spinocalanidae).
2- Mandibular endopod segment 1 lacking setae (vs. 2-4 setae in Spinocalanidae).
3- Distal basal endite and endopod of Mx1 are usually fused with 4 or less (without any setae in Caudacalanus and Foxtonia) vs. distal endite supplied with 1-6 and endopod with 7-16 setae in Spinocalanidae, partly or completely separate (fused in Isaacsicalanus).
4- Ptoximal coxal endite of Mx2 with fewer than 3 setae (vs.3 setae in Spinocalanidae).
5- Terminal segment of Mxp endopod with fewer than 4 setae (vs. 4 setae in Spinocalanidae).
6- P1 medial seta of basis and lateral lobe of endopod absent (vs. present in Spinocalanidae).

Among the Spinocalanoidea, the Arctokonstantinidae are characterized by a reduced segmentation and setation of the oral parts and P1, and appear to be more than the Spinocalanidae.
Three genera (Foxtonia, Sognocalanus, Arctokonstantinus are pelagic deep-water inhabitants, Caudacalanus is benthopelagic. Arctokonstantinidae is a later offshoot of the Spinocalanids, but it is difficult to speculate if its ancestor was primarily pelagic and invaded the near-bottom secondarily, or was benthopelagic and then invaded the open water column.
Family Arctokonstantinidae - Plate 1issued from : E.L. Markhaseva in Russian J. Mar. Biol., 2008, 34 (1). [p.15].
Details of armament of mouthparts and P1 in the family.
The table presents the most primitive condition of characters that has been revealed for the genus. Synapomorphies for genera placed into the family are shown in boldface.
Nota: The author concludes that Arctokonstantinus, Sognocalanus, Foxtonia, and Foxtosognus together comprise a monophyletic group of genera within the superfamily Spinocalanoidea. This group is characterized by reduction of the number of setae on mouthparts, the loss of seta on the basis and loss of the lobe of the endopod in P1, and, often, also by fusion together of the basis and endopod of Mx1. In addition, the following apomorphies have been revealed that distinguish the family Arctokonstantinidae: the basis of mandibular palp bears 1 or 2 setae (there are 3 to 4 setae in Spinocalanidae); the 1st segment of endopod of mandibular palp is lacking setae (there are 2 to 4 setae in Spinocalanodae); the distal endite of basis and endopod of Mx1 together bear 2 to 4 setae or are lacking setae (Foxtonia) (there are 8 to 21 setae in Spinocalanidae).
(1) Arctokonstantinus Markhaseva & Kosobokova, 2001
Ref.: Markhaseva & Kosobokova, 2001 (p.320); Boxshall & Halsey, 2004 (p.198); Markhaseva, 2008 (p.15, Rem.).
Rem.: Type: Arctokonstantinus hardingi Markhaseva & Kosobokova, 2001. Total: 1 sp.
Considered as a type of a new family (Arctokonstantinidae) by Markhaseva & Kosobokova (2001, p.319), placed among the Spinocalanidae par Boxshall & Halsey (2004, p.196, 198).

Diagnosis after Markhaseva & Kosobokova (2001, p.320):
Female:
- Rostrum absent.
- Cephalon and 1st pedigerous seomite incompletely separate, 4th and 5th pedigerous somites separate.
- Urosome 4-segmented.
- Genital segment symmetrical.
- A1 24-segmented.
- A2 exopod incompletely 8-segmented (exopodal segments 2-3 partly fused), shorter than endopods (endopodal segment 1 with 1 seta).
- Md endopodal segment 1 without seta, endopodal segment 2 with 6 setae.
- Mx1 inner lobe 4 without setae (as Rhinomaxillaris), endopod rudimentary with 4 setae.
- P1 endopod without outer lobe and basis without inner setae (as Sognocalanus).
Remarks on dimensions and sex ratio:
Body size in only one female: 4.1 mm. Male unknown
(2) Caudacalanus Markhaseva & Schulz, 2008
Ref.: Markhaseva & Schulz, 2008 a (p.278); Renz & Markhaseva, 2015 (p.96, Table 4, fig.3, biogeography)
Rem.: type: Caudacalanus mirus. Total: 2 spp.
Remarks on dimensions and sex ratio:
The mean female size is 2.325 (n = 4; SD = 0.4992). Male unknown.
(3) Foxtonia Hulsemann & Grice, 1963
Ref.: Hulsemann & Grice, 1963 (p.733); Razouls, 1982 (p.593); Fosshagen, 1983 (p.260); Razouls, 1993 (p.308); Mauchline, 1998 (p.66); Boxshall & Halsey, 2004 (p.198); Markhaseva, 2008 (p.10, 15, 14, Rem.: p.12)
Rem.: Originally included, with doubt, in the Bathypontiidae. For Schulz (1996, p.599) this genus could be included among the Spinocalanidae. Position followed by Boxshall & Halsey, 2004 (p.196, Rem.), but genus considered by Markhaseva (2008) as belonging to the family Arctokonstantinidae.
1 sp.
(4) Foxtosognus Markhaseva, 2008
Ref.: Markhaseva, 2008 (p.10, 14, 15)
Rem.: Type: Foxtosognus rarus Markhaseva, 2008. Total: 1 sp.

Diagnosis from Markhaseva (2008, p.9):
Female:
- Rostrum in short plate, rounded.
- Caudal rami symmetrical, their inner setae arranged symmetrically.
- A1 short, somewhat longer than cephalosome.
- A2 endopod longer and thicker than exopod; 2nd exopodal segment with 1 seta.
- Md basis of palp with 2 setae; 1st endopodal segment longer than 2nd segment, which is provided with 7 setae; terminal segment of exopod with 2 setar; gnathobase with 3 teeth and 2 setae.
- Mx1 praecoxal arthrite with 7 to 8 setae; both coxal and ptoximal basal endites reduced; distal basal endite without setae and separated from endopod with 3 setae; exopod with 4 setae.
- Mx2 proximal and distal endites of praecoxa with 3 and 2 setae, respectively; proximal and distal endites of coxa with 2 and 3 setae, respectively; those of basis with 3 and 2 setae, respectively; endopod with 4 setae.
- Mxp praecoxal endites of syncoxa lacking setae; coxal endite with 1 seta; allobasis with 1 seta arising in the middle part of segment and 2 setae locared distally; endopod 3-segmented, its segments have 1, 3, and 2 setae, respectively.
- P1 exopod 3-segmented, each segment with 1 external spine.
- P2 endopod 2-segmented.
- P3-P4 endopods 3-segmented, 3rd segment bears 6 setae.

Male unknown.

For Markhaseva, the new genus shows more morphological similarities to genera Foxtonia and Sognocalanus.
Remarks on dimensions and sex ratio:
The body size for only one female is 2.7 mm.
(5) Sognocalanus Fosshagen, 1967
Ref.: Fosshagen, 1967 (p.308, 313); Razouls, 1982 (p.594); Fosshagen, 1983 (p.260); Razouls, 1993 (p.309); Schulz, 1996 (p.599, Rem.); Mauchline, 1998 (p.87: F; p.90: M); Markhaseva & Kosobokova, 2001 (p.319, 323, Rem.); Boxshall & Halsey, 2004 (p.198); Markhaseva, 2008 (p.10, 12, 14, Rem.: p.15)
Rem.: Formerly included in the Bathypontiidae family, but considered by Markhaseva (2008) as belonging to the family Arctokonstantinidae.
Total: 1 sp.

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Razouls C., Desreumaux N., Kouwenberg J. and de Bovée F., 2005-2021. - Biodiversity of Marine Planktonic Copepods (morphology, geographical distribution and biological data). Sorbonne University, CNRS. Available at http://copepodes.obs-banyuls.fr/en [Accessed December 01, 2021]

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