Mixtodiaixis kurambiohadalis sp. nov.

urn:lsid:zoobank.org:act: 3519F23C-704F-43A7-890D-CEBA0B7B5FF8

(Figs. 1–7)

Holotype, adult female, dissected, body length 1.30 mm. SMF 37282 /1 (vial) and 37282/2–5 (slides), collected at Sta. 89, 44°39.33’ N 151°27.34’ E on 16 September 2016 at a depth of 8215 m.

Paratypes: one adult male, dissected, body length 1.15 mm, SMF 37283 /1 (vial) and 37283/2–5 (slides), the same label data as for the holotype; two females, dissected, body length 1.30–1.35 mm, ZIN 91183 (vial and slides), collected at Sta. 40, 45°40.69’ N 152°57.37’ E on 29 August 2016 at a depth of 7060 m; one female, dissected, body length 1.30 mm and one male, dissected, body length 1.20 mm, ZIN 91184 (vial and slides), collected at Sta. 42, 45°40.17’ N 152°57.46’ E on 30 August 2016 at a depth of 7122 m.

Additional material. One female, collected at Sta. 55, 45° 29.49’ N 153°12.54’ E on 06 September 2016, at depth 8740 m and one male, Sta. 102, 44° 11.99’ N 150°34.77’ E on 20 September 2016, at depth 9537 m

Description. Female. Body length 1.30–1.35 mm. Prosome 3.1–3.3 times as long as urosome (Fig. 1A–B). Rostrum (Fig. 1C–D) as a bilobed plate. Cephalosome and pedigerous somite 1 and pedigerous somites 4–5 separate; posterior corners of prosome as a lobes, reaching the posterior third of genital double-somite (Fig. 1A–B, E–F). Urosome of 4 somites. Genital double-somite symmetrical (Fig. 1E). Spermathecae oval and slightly widened in the distal part (Fig. 1F–H). Caudal rami with 1 ventral seta and 4 terminal setae, lateral seta have not been observed (Fig. 1E–F).

Antennule (Fig. 2A–D) reaching pedigerous somite 5, or as long as prosome, of 24 articulating segments; armature as follows: I-3?, II–IV-6s+1ae, V-2s, VI-2s, VII-1s+1ae+1?, VIII and IX-2s each, X–XI-4?, XII and XIII-1s each, XIV-2s+1ae, XV-1s, XVI-2s+1ae, XVII to XVIII-1? each, XIX-1?, XX-2s, XXI to XXII-1? and XXIII-1s+1?, XXIV-2s, XXV–XXVI-1s+1? each, XXVII–XXVIII-5s+1ae. Row of tiny spinules present along the lateral anterior border of ancestral segments I, IX, XVI to XVIII, and XXIII–XXIV, supplied by row of tiny spinules along their anterior margin laterally.

Antenna (Fig. 2E–G), coxa with 1 seta, basis with 2 setae; exopod of 8 segments, setation formula 0,0-0-0, 1, 1, 1, 1, 1, and 3 setae, complex segment, following proximal segment with small hump laterally (arrowed) and tiny spinules medially; endopod segment 1 with 1 setae, endopod segment 2 with 6 + 6 or 7 setae.

Mandible (Fig. 2H–J), gnathobase with 5 teeth and 4 setae (arrowed); 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.

Maxillule (Fig. 3A), praecoxal arthrite with 7 terminal spiniform setae, posterior and anterior setae absent, coxal endite with 2 setae; coxal epipodite with 9 setae; proximal basal endite with 4 setae, distal basal endite with 4 setae; endopod with 8 setae; exopod with 7–8 setae.

Maxilla (Fig. 3B–E), praecoxal endite with 4 setae; coxal endite with 3 setae; proximal basal endite with 3 setae, 1 sensory; distal basal endite with 3 setae, 1 sensory, poorly sclerotized; enditic-like lobe of proximal endopod segment with 4 setal elements, 1 robust spine, 1 long seta and 2 sensory worm-like setae, and endopod with 9 setae, 3 worm-like and 6 brush-like.

Maxilliped (Fig. 3F, 4A–B), syncoxa with 1 worm-like sensory seta on proximal praecoxal endite, 2 setae on middle praecoxal endite (1sc+lw), and 3 setae on distal praecoxal endite 1 sclerotized long, 1 sclerotized small and 1 sensory, brush-like, i.e. setal formula is 1w+(1sc+1w)+(2sc+1br); coxal lobe with 2 setae and very small tubercle (arrowed at Fig. 4A),. Basis with 3 proximal and 2 distal setae partly separated, tiny spinules present medially from proximal to distal. Endopod 5-segmented, with 3, 4, 2, 2+1, and 4 setae.

Legs. P1 (Fig. 4C–E), coxa with lateral spinules and spinules anterior-laterally; basis with medial distal seta curved, anterior small spines along distal border and surface; endopod 1-segmented with poorly developed lateral lobe; exopod segments 1 to 3 with 1 lateral spine each; lateral spine of exopod segment 1 exceeding the base of the lateral spine at the exopod segment 2 and nearly reaching the half length of the exopod segment 3.

P2–P4 (Fig. 5A–F), coxa with 1 medial seta, P2-P3 coxa with posterior and lateral spinules, at P4 coxa lateral spinules short; basis without seta; endopod 2-segmented in P2, 3-segmented in P3–P4. P2 endopod segment 1 with 2 posterior spines and scarce posterior spinules; endopod segment 2 with about 6 posterior spines and posterior spinules; exopod segments 1 to 3 with posterior spinules. P3 endopod and exopod segments with posterior spinules. P4 endopod segments 1 to 3 with posterior spinules.

P5 present (Fig. 1I–J), uniramous, 3-segmented; coxal segments with spinules anteriorly and laterally; basipod segments densely covered with posterior spinules; exopod one-segmented, densely covered with posterior spinules.

Male. Body length 1.15, 1.20 mm. Prosome 2.9–3.2 times as long as urosome. Rostrum as in female. Cephalosome and pedigerous somite 1 separate, somites 4–5 partly separate (Fig. 6A–B). Сephalosome lateral anterior margin with triangular extensions in dorsal view; posterior corners of prosome as a lobes, in lateral view reaching the middle length of urosome somite 2 (Fig. 6B–D). Urosome of 5 somites. Caudal rami with 1 ventral seta and 4 terminal setae, lateral seta have not been observed (Fig. 6C–D).

Antennule, right (Fig. 7A–E) reaching urosome somite 4, of 23 articulating segments; armature as follows: I-1s+1ae+1?, II–IV-6s+3ae, V-1s+2ae, VI-2s+1ae, VII-2s+2ae, VIII-1s+1ae, IX-2s+2ae, X–XI-3s+3ae, XII-1?, XIII-2?, XIV-1ae+1?, XV-1s+2ae, XVI-1, XVII-1s, XVIII-1ae+1?, XIX-1?, XX-1+1ae, XXI-1s+1ae, XXII–XXIII-1s, XXIV-2s+1ae, XXV–XXVI-2s each, XXVII–XXVIII-5s+1ae.

Antenna, mandible, maxillule, maxilla (Fig. 7F) and maxilliped nearly identical to that of female, only hump on the complex segment of antenna more pronounced (Fig. 6E); mandible basal palp setae shorter, and endopod segment 1 lacking setae.

Legs. P1 (Fig. 6F), coxa, basis and exopod as in female; endopod differs in Vaupel Klein’s organ (Fornshell and Ferrari, 2014), i.e., endopod lobe reduced, basal medial seta not curved; lateral spinulation present at endopod medially.

P2–P4 as in females.

P5 (Fig. 6G–H) present, uniramous of simple structure; right and left segments of coxa and basis asymmetrical, exopods 3-segmented; right exopod segment 3 with 2 spines, one long and one short; left exopod segment 2 with medial anterior thin spine and exopod segment 3 with thin terminal spine and 4 terminal spinules.

Type locality. 44° 39.33’ N 151°27.34’ E; depth: 8215 m.

Etymology. The species name “ kurambiohadalis ” refers to the name of the expedition KuramBIO and the hadal habitat of the species in the Pacific Ocean.