Byrathis arnei Schulz, 2006

Markhaseva, Elena L. & Renz, Jasmin, 2011, Two new Byrathis species (Copepoda: Calanoida) from the deep South Atlantic and Southern Ocean and first description of an adult male, Zootaxa 2889, pp. 49-68 : 61-66

Byrathis arnei Schulz, 2006

( Figs 10–13 )

Material. 12 adult females, body length 1.25–1.35 mm, and 9 adult males, body length 1.40–1.55 mm collected above the sea bed by the ANDEEP–SYSTCO expedition at a depth of 2152 m, on 0 4 January 2008 in the South Ocean (64º29’S 02º53’E) and 23 adult females, body length 1.33–1.67 mm, from 3 samples obtained by ANDEEP II–III expeditions at depths from 2006 to 3050 m between 58–65ºS and 25–64ºW.

Description. Male. Prosome 2.30–2.75 times as long as urosome. Rostrum a plate with 2 filaments ( Fig. 10 A). Cephalosome and pedigerous somite 1 fused, pedigerous somites 4 and 5 separate; posterior corners rounded. Urosome of 5 somites, anal segment very short ( Fig. 10 A–B). Caudal rami with 4 terminal setae, 1 ventral seta and 1 dorsolateral seta.

Antennule ( Fig. 10 C–E) extending to anterior, or posterior edge of urosome somite 2. Right and left antennules of 22 articulating segments, symmetrical; armature as follows: I–1 s + 1ae, II– IV–6 s + 4ae, V–2 s + 2ae, VI–2 s + 1ae, VII–2 s + 2ae, VIII–1 s + 1ae + 1?, IX–2 s + 2ae, X– XII–3 s + 1? + 2ae, XIII–1s, XIV–2s, XV–1s, XVI–1s + 1ae, XVII–1s, XVIII–1s, XIX–1s, XX–1s, XXI–1s, XXII–XXIII–1s, XXIV–2s, XXV–2s, XXVI–2s, XXVII– XXVIII–4s + 1ae.

Antenna ( Fig. 11 A), coxa with 1 seta, basis with 2 setae, 1 very small; exopod 8-segmented with 1, 1-1-1, 1, 1, 1, 1, 1, and 3 setae; first endopodal segment without seta, second with 6 + 7 setae.

Mandible ( Fig. 11 B–C), gnathobase with low crest and 7 teeth on cutting edge plus dorsal seta, lateral tooth situated apart from the remaining teeth; basis with 2 rudimentary setae; exopod 5-segmented with 1, 1, 1, 1, and 2 setae; endopod segment 1 with 2 setae, segment 2 with 9 setae.

Maxillule ( Fig. 11 D), praecoxal arthrite with 9 terminal; coxal endite with 2 setae; proximal basal endite with 2 setae, distal basal endite with 2 setae; endopod with 7 setae; exopod with 5 setae; coxal epipodite with 4 setae.

Maxilla ( Fig. 11 E), praecoxal endite (previously considered as proximal praecoxal endite) with 4 setae; coxal endite (previously considered as distal praecoxal endite) with 3 setae; proximal basal endite (previously considered as proximal coxal endite) with 2 setae; distal basal endite (previously considered as distal coxal endite) with 3 setae; enditic-like lobe of proximal endopodal segment (previously considered as proximal basal endite) with 4 setae, 2 sensory; endopod with 5 worm-like and 3 brush-like sensory setae.

Maxilliped ( Fig. 12 A–B), syncoxa with 1 seta on proximal praecoxal endite, 1 seta on middle praecoxal endite, and 1 brush-like seta on distal praecoxal lobe; coxal lobe with 2 setae. Basis with 3 setae. Endopod 6-segmented with 2, 4, 4, 3, 3, and 4 setae.

Swimming legs. P1 ( Fig. 12 C), coxa with anterior row of small spinules along distal margin; basis with medial distal seta slightly curved with setules; endopod 1-segmented with lateral lobe lacking spinules; exopod segments 1 to 3 with 1 lateral spine each, spine of segment 1 nearly reaching base of following spine; spine of exopod segment 2 reaching midlength of exopod segment 3. P2 ( Fig. 12 D), coxa with 1 seta; basis without seta; endopod 2-segmented; exopod 3-segmented; exopod segment 2 with 3 small surface denticles along distomedial edge. Endopods and exopods 2–3 in P3–P4 of all male specimens broken, coxa of P3–P4 ( Fig. 12 E–F) with small proximal spinules laterally, basis and segment of 1exopod and endopod nude.

P5 ( Fig. 10 A, 13A–C) nearly half as long as the urosome, legs of about equal lengths; in left coxa and basis only slightly longer than right. Right leg uniramous, exopod 3-segmented; left leg biramous, exopod 3-segmented, distal segment with subdivided chitinous lamella; endopod 1-segmented, much longer than exopod.

Remarks. B. arnei was described after females from the near-bottom of the high Antarctic (74º36.2’S 27º15.8’S) by Schulz (2006) and in the present study is recorded more northerly ( Fig. 9 ). The species was collected by ANDEEP II–III and ANDEEP–SYSTCO expeditions (2002, 2005, 2007–2008) between 58º–65ºS and 02ºE– 51ºW at depths from 1991 to 3050 m. One sample from ANDEEP–SYSTCO contained Byrathis females and males. We attribute them to B. arnei , although they differ somewhat from females defined as B. arnei by Schulz (2006) and specimens studied by us. Females from the ANDEEP–SYSTCO sample differ in: i) smaller size (1.25– 1.35 mm vs. 1.38–1.40 mm in type specimens); ii) maxillule coxal epipodite with 8 setae (vs. 9 setae in specimens from the type series); iii) maxilla praecoxal endite with 4 setae (vs. 5 setae in type specimens), and iv) distal seta on middle praecoxal endite of maxilliped syncoxa is slightly longer than figured for type specimen (Schulz 2006, Fig.10 A). However, we would prefer to postpone the discussion on the taxonomic status of the specimens from the ANDEEP–SYSTCO, until more specimens of B. arnei can be obtained. Additional collections from different localities are necessary to discuss whether the variability observed is interspecific, or whether a new species should be established for ANDEEP–SYSTCO specimens.

Figures

FIGURE 9. Distribution of species of Byrathis in the World Ocean: black rhomboid B. macrocephalon (Grice & Hulsemann, 1970); circle outlined, B. penicillatus sp. nov.; black square, B. laurenae Markhaseva & Ferrari, 2005; big triangle outlined, B. arnei Schulz, 2006; black small triangle, B. divae sp. nov.; rhomboid outlined, B. laptevorum (Markhaseva, 1998); rhomboid outlined with crest, B. volcani Markhaseva & Ferrari, 2005.

FIGURE 10. Byrathis arnei Schulz, 2006. Male. A, habitus, lateral view, rostrum, ventral view, marked by arrow; B, habitus, dorsal view; C, antennule, articulating segments 1 – 9 (ancestral segments I – XIII); D, antennule, articulating segments 10 – 17 (ancestral segments XIV – XXI); E, antennule, articulating segments 18 – 22 (ancestral segments XXII – XXVIII). Scale bars 0.1 mm.

FIGURE 11. Byrathis arnei Schulz, 2006. Male. A, antenna; B, mandubular palp; C, mandibular gnathobase; D, maxillule; E, maxilla. Scale bars 0.1 mm.

FIGURE 12. Byrathis arnei Schulz, 2006. Male. A, maxilliped, basis and endopod; B, maxilliped, syncoxa; C, P 1; D, P 2; E, P 3, coxa, basis, segment 1 of endopod and exopod; F, coxa, basis, segment 1 of endopod and exopod. Scale bars 0.1 mm.

FIGURE 13. Byrathis arnei Schulz, 2006. Male. A, P 5; B, left P 5 endo- and exopod, other specimen; C, right P 5 exopod, other specimen. Scale bar 0.1 mm.