Species Card of Copepod
Calanoida ( Order )
    Clausocalanoidea ( Superfamily )
        Diaixidae ( Family )
            Byrathis ( Genus )
Byrathis macrocephalon  (Grice & Hulsemann, 1970)   (F)
Syn.: Xanthocalanus macrocephalon Grice & Hulsemann, 1970 (p.191, Descr.F, figs.F); Bradford, 1973 (p.139, 147, Rem.); Bradford & al., 1983 (p.127); Schulz & Beckmann, 1995 (p.210, Rem.);
Tharybis macrocephalon: Ferrari & Markhaseva, 2005 (Rem.: p.33; p.46: tab.1, Rem.)
Ref.:
Markhaseva & Ferrari, 2005 a (p.139, figs.F, tab.2, Rem..)
Species Byrathis macrocephalon - Plate 1 of morphological figuresissued from : E.L. Markhaseva & F.D. Ferrari in Invert. Zool., 2005, 2 (2). [p.142, Fig.18].
Female (from holotype): A, posterior prosome and urosome (lateral, right side); B, A2 (exopod); C-D, Md (gnathobase; posterior and proximal, respectively); E, Mx2 (praecoxal, coxal and proximal basal endites); F, Mx2 (sensory setae of distal basal endite + ramus); ; G, Mxp (syncoxa); H, P1 (distal part of basis and endopod; anterior).
Scale bars: 0.1 mm.

Nota: Prosome 4.6-5.4 times longer than urosome.
- Cephalosome fused with pediger 1, pedigers 4 and 5 fused dorsally, separate laterally.
- Anterior cephalosome rounded dorsally.
- Posterior corners of prosome produced into short, indented lobe in lateral view.
- Genital complex symmetrical, spermathecae elongate, dorsal part directed dorsally.
- Rostrum: 2 short, thin filaments.
- A1 24-segmented.
A2 coxa with 1 seta; basis with 2 setae; endopod 2-segmented, proximal segment with 1 seta; distal with 14 (6 terminal and 8 sub-terminal setae); exopod 8-segmented with 1, 3, 1, 1, 1, 1, 1, 3 setae.
- Md gnathobase with tooth-like knob on posterior face, cutting edge wide with 8 teeth and 1 seta; basis with 3 setae; endopod 2-segmented, proximal with 2 setae, distal with 9 setae; exopod with 1, 1, 1, 1, 2 setae.
- Mx1 praecoxal endite with 2 posterior and 9 terminal setae, proximal 2 terminal setae curved proximally; coxal endite with 2 setae, coxal epipodite with 7 setae; proximal basal endite with 2 setae, distal with 3 setae (1 of them small); endopod with 7 setae in groups of 2+5; exopod with 4 setae.
- Mx2 proximal praecoxal endite with 4 setae, distal with 3 setae, 1 thicker; proximal coxal endite with 3 setae, 1 thicker; distal with 3 setae, 1 thicker; proximal basal endite with 4 setae, 1 thicker, 1 worm-like; distal basal endite +ramus with 5 worm-like and 3 brush-like sensory setae, 1 brush-like seta thicker and with longer setules.
- Mxp praecoxal endites of syncoxa with 1, 2, 3 setae, 1 worm-like; coxal endite with 3 setae; basis with a row of small denticles proximally, 3 medial setae, 2 setae on distal endite; endopod of 5 segments with 4, 4, 3, 3+1 lateral and 4 setae.
- P1 coxa without seta; basis with medial seta; endopod with 3 medial and 2 terminal setae; Von Vaupel Klein's organ with basal seta slightly curved, anterior knob rounded and with denticles; exopod 3-segmented, proximal with 1 lateral seta, middle with 1 medial and 1 lateral seta, distal with 3 medial, 1 terminal, 1 lateral seta; lateral seta on proximal segment exceeds the base of lateral setae of following segment, lateral seta on middle segment exceeds half length of lateral seta of terminal segment.
- P2-P4 as described by Grice & Hulsemann (1970).
- P5 3-segmented: exopod (distal segment) with 1 long medial and 1 short lateral setae, and 1 subterminal and 1 terminal attenuation.
- Caudal rami with 4 large, thick terminal setae, 1 small dorsal seta and 1 small medial ventral seta.


Species Byrathis macrocephalon - Plate 2 of morphological figuresissued from : E.L. Markhaseva & F.D. Ferrari in Invert. Zool., 2005, 2 (2). [p.137, Table 2].
Byrathis macrocephalon (Selected character states of species included in Byrathis gen. n.).
Ce = cephalosome; Mn = mandible; Pd = pediger segment; Ri = endopod; Re = exopod


Species Byrathis macrocephalon - Plate 3 of morphological figuresissued from : E.L. Markhaseva & F.D. Ferrari in Invert. Zool., 2005, 2 (2). [p.138, Table 2 (contituing)].
Byrathis macrocephalon (Selected character states of species included in Byrathis gen. n.).
Ri = endopod; Re = exopod.


Species Byrathis macrocephalon - Plate 4 of morphological figuresIssued from : G.D. Grice & K. Hülsemann in Bull. Mus. Comp. Zool., Harvard, 1970, 139 (4). [p.208-209, Pl. VI, Figs. 111-116]. As Xanthocalanus macrocephalon.
Female (from 39°45.2'N, 70°33.8'W): 111-112, habitus (lateral and dorsal, respectively); 113, forhead (lateral); 114, same (ventral); 115, 5th thoracic segment and urosome (lateral); 116, right A1.

Nota : - Head and 1st thoracic segment fused, separation indicatd laterally by short line, 4th and th seggment incompletely separated.
- Abdomen 4-segmented.
- Rostrum small without filaments.
- Posterolateral margin of 5th thoracic segment angular.
A1 reaching end of cephalothorax, segments 8 and 9 fused.
- Exopod of A2 twice the length of endopod.
- Basal segment of Md palp with 3 setae ; conspicuous hump on external side of Gnathobase ; teeth on chewing edge small.
- Mx1 with 1st inner lobe bearing 10 spines, 2nd and 3rd inner lobes and 2nd basal segment each with 2 setae , 2 and 5 setae on endopod, 4 setae on exopod.
- Mx2 1st lobe with 4 setae, 2nd to 4th lobes each with 3 setae, 5th lobe with 3 setae, 1 small spine and 1 sensory appendage ; endopod with 2 types of sensory appendages.
- Endopod of P1 1-segmented, of P2 2-segmented, of P3 to P4 3-segmented ; exopods of all four legs 3-segmented. In P2 to P4 posterior sides of endopods armed with spinules, in P4 also basipod and exopod.
- P5 3-segmented, on posterior side, mainly externally, covered with small spines. Terminal segment with 1 small external spine, 1 long internal spine and 2 terminal points, not articulating with the segment.


Species Byrathis macrocephalon - Plate 5 of morphological figuresIssued from : G.D. Grice & K. Hülsemann in Bull. Mus. Comp. Zool., Harvard, 1970, 139 (4). [p.210-211, Pl. VII, Figs. 117-127]. As Xanthocalanus macrocephalon.
Female: 117, A2; 118, Md palp; 119, Md (masticatory edge); 120, Mx1; 121, Mx2; 122, Mxp; 123, P1; 124, P2; 125, P3; 126, P4; 127, P5.

NZ: 1

Distribution map of Byrathis macrocephalon by geographical zones
Loc:
NW Atlant. (off Woods Hole).

Type locality: 39°45.2' N, 70°33.8' W.
N: 1
Lg.:
(200) F: 1,12-1,06; {F: 1,06-1,12}
Rem.: For Markhaseva & Ferrari (2005, p .141) this species can be distinguished from B. volcani by the size ; 3 setae on basis of Md (2 setae in B. volcani) ; distal to anterior knob of Vaupel Klein’s organ of P1 bears denticles (without denticles on B. volcani) ; and distinguished from B. laurenae by the symmetrical genital complex (slightly asymmetrical in B. laurenae ; 8-segmented exopod of A2 (7-segmented for B. laurenae) and elongate segment with 3 setae (4 setae for B. laurenae.
According to Schulz (2006, p.67) Xanthocalanus laptevorum should be incorporated within Byrathis particularly on account of characters of A2, Md, Mxp, P1 and P5.
Last update : 28/03/2016
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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 July 01, 2022]

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