Byrathis penicillatus, Markhaseva, Elena L. & Renz, Jasmin, 2011

Byrathis penicillatus sp. nov.

( Figs 5–9 View FIGURE 5 View FIGURE 6 View FIGURE 7 View FIGURE 8 View FIGURE 9 )

Holotype. Partly dissected adult female, body length 4.05 mm. ZMH Reg. no. K–42157. Collected on 15 March 2005 by the DIVA –II expedition above the sea bed at abyssal depths ( 5058 m).

Paratypes, 1 partly dissected adult female, body length 3.95 mm. ZMH Reg. no. K–42158. Collected on 15 March 2005 by the DIVA –II expedition above the sea bed at abyssal depths ( 5050 m) in the South Atlantic ( 00º08.5’S 02º30.2’W); 1 partly dissected adult female, body length 3.35 mm. ZIN –91103. Collected 23 July 2009 by the DIVA –III expedition in the South Atlantic ( 26º35’S 35º14’W), above the sea bed at abyssal depths ( 4482– 4489 m). Additional material: 4 females, body length 3.20–4.90 mm, collected in the South Atlantic from the equator to about 36ºS at depths from 4601 to 5395 m.

Type locality. South Atlantic ( 00º01.2’S, 02º28.7’W).

Description. Female. Body length 3.35–4.90 mm. Prosome 3.7–4.1 times as long as urosome. Rostrum as a triangular plate with 2 filaments ( Fig. 5 View FIGURE 5 C–D). Cephalosome and pedigerous somite 1 and pedigerous somites 4 and 5 partly separate; posterior corners sharply triangular in dorsal and lateral view ( Fig. 5 View FIGURE 5 A–B, E–G). Urosome of 4 somites. Caudal rami with 4 terminal setae, 1 ventral seta and 1 small dorsolateral seta ( Fig.5 View FIGURE 5 E–F).

Antennule ( Fig. 6 View FIGURE 6 A–C) extending to distal margin of pedigerous somites 4–5, of 24 articulating segments; armature as follows: I–3 s, II– IV–6 s + 1ae, V–2 s + 1ae, VI–2 s, VII–2 s + 1ae, VIII–1 s+1?, IX–2 s + 1ae, X– XI–4 s + 1ae, XII–1?, XIII–1?, XIV–2s + 1ae, XV–1?, XVI–2s + 1ae, XVII–1?, XVIII–2?, XIX–1?, XX–2?, XXI–1s + 1ae, XXII–1?, XXIII–1s, XXIV–1s + 1?, XXV–2s, XXVI–2s, XXVII–XXVIII–4s + 1ae, (setation on Fig. 6 View FIGURE 6 A–C is given for segments II–IV, VI, VII, IX–XI, XIV, XVI and XXIII after the holotype and supplemented from the paratypes).

Antenna ( Fig. 6 View FIGURE 6 D), coxa with 1 seta, basis with 2 setae; exopod of 7 free segments with 1, 1-1-1-1, 1, 1, 1, 1, and 3 setae, seta on proximal exopod segment rudimentary, following complex segment with 3 rudimentary setae, partly fused with first short segment bearing long seta; first endopodal segment with 2 setae, second with 8 + 7 setae.

Mandible ( Fig. 6 View FIGURE 6 E–G), gnathobase with crest, number of teeth on cutting edge of holotype difficult to follow, paratype bearing 4 large and 3 small teeth near dorsal seta, lateral tooth situated apart from the remaining teeth; basis with 3 setae; exopod 5-segmented with 1, 1, 1, 1, and 2 setae; endopod segment 1 with 2 setae, segment 2 with 9 setae and distal rows of small surface spinules.

Maxillule ( Fig. 6 View FIGURE 6 H–I), praecoxal arthrite with 9 terminal, 4 posterior, and 1 anterior setae; coxal endite with 2 setae; coxal epipodite with 9 setae; proximal basal endite with 3 setae, distal basal endite with 3 setae; endopod with 9 setae; exopod with 8 setae.

Maxilla ( Fig. 7 View FIGURE 7 A–C), praecoxal endite (previously considered as proximal praecoxal endite) with 4 setae and a short attenuation; coxal endite (previously considered as distal praecoxal endite) with 3 setae; basal endites (previously considered as coxal endites) with 3 setae each, 1 seta on the proximal basal endite very short, 1 seta on distal basal endite very strong, spine-like, enditic-like lobe of proximal endopodal segment (previously considered as proximal basal endite) with 4 setae, 1 is thicker and 1 is sensory; all endites with a patch of long spinules at the base of the setae; endopod with 3 worm-like and 5 brush-like sensory setae: 2 setae shorter with large brushes, 3 setae longer with smaller brushes.

Maxilliped ( Fig. 7 View FIGURE 7 D), syncoxa with 1 seta and a row of spinules on proximal praecoxal endite, 2 setae (1 sensory in distal part) and a patch of spinules on the middle endite and 2 sclerotized and 1 large brush-like seta on the distal praecoxal endite; coxal endite with 3 setae. Basis with 3 setae, proximal row of long spinules extended to the proximal basal seta and row of small spinules extended from the proximal to the distal-most basal seta. Endopod 6- segmented with 2, 4, 4, 3, 3+1, and 4 setae.

Swimming legs. P1 ( Fig. 8 View FIGURE 8 A), coxa with anterior row of spinules along the distal margin; basis with medial distal seta strongly curved with setules; endopod 1-segmented with lateral lobe, its lateral margin with spinules; exopod segments 1 to 3 with 1 lateral spine each, spine of segment 1 reaching base of following spine; spine of exopod segment 2 not reaching the base of distal-most spine. P2–P4 ( Fig. 8 View FIGURE 8 B–D), coxa with 1 seta; basis without seta; endopod 2-segmented in P2, second segment on posterior surface with patch of long spinules; exopods 3-segmented. Endopods 3-segmented in P3–P4, segment 2 with a patch of long spinules on the posterior surface, segment 3 posterior surface densely spinulate, although with shorter spinules. Posterior surface of P4 coxa, basis and exopod densely spinulate.

P5 ( Fig. 7 View FIGURE 7 E) 3-segmented, coxa and basis of equal length; coxa and basis with a patch of minor spinules distolaterally; exopod ornamented with surface spinules, 4 distal spines, medial terminal spine is curved, about 1.7 times longer than lateral terminal spine.

Etymology. The species name “ penicillatus ” refers to a large brush-like sensory seta on the syncoxa of the maxilliped.

Remarks. B. penicillatus sp. nov. is more closely related to its most geographically distant congener B. laptevorum ( Fig. 9 View FIGURE 9 ) and shares with this species the following distinguishing characters: i) maxilla distal basal endite (previously considered as distal coxal endite) and enditic-like lobe of proximal endopodal segment (previously considered as proximal basal endite), each with 1 very strong, spine-like setal element ( vs. these setal elements are neither strong nor spine-like in congeners); ii) each maxilla endite with a patch of long surface spinules ( vs. surface spinule patch is absent in the other species of the genus); iii) medial praecoxal endite of maxilliped syncoxa with a patch of spinules ( vs. no spinule patch in congeners).

B. penicillatus sp. nov. differs from B. laptevorum in: i) large brush-like sensory seta on distal praecoxal endite ( vs. poorly developed brush in B. laptevorum ); ii) maxilliped basis with a patch of long spinules proximally ( vs.

spinules absent in B. laptevorum ), and iii) P5 medial terminal spine curved, about 1.7 times longer than lateral terminal spine ( vs. straight spine, nearly twice as long as lateral terminal spine in B. laptevorum ). Maxilla endopod of single known specimen of B. laptevorum is described as bearing 1 worm-like sensory seta ( vs. 3 brush-like setae in B. penicillatus sp. nov.), but this character should be re-examined for the species when new specimens of B. laptevorum are obtained.