Cerviniella arctica Kihara & Arbizu, 2012, sp. nov.

Cerviniella arctica sp. nov.

(Figs 6 C–E, 7–10, 18–19)

Type locality. Arctic Ocean, Laptev Sea (78°23.19' N, 133°11.43' E), 2019 m depth.

Type material. Holotype female dissected on 14 slides (reg. no. SMF 37030) from station PS27#035/2457-1, multi corer 5, collected 04/09/1993. Material collected from the type locality by the junior author during the Expedition ARCTIC’93, Leg ARK-IX/4 of RV Polarstern.

Description. FEMALE. Total body length 1014.7 μm. Largest width measured at posterior border of cephalic shield: 352.9 μm. Body (Figs 6 C, 18A–C) with no clear distinction between prosome and urosome, body somites gradually tapering posteriorly.

Prosome (Figs 6 C, 18A–C) 4-segmented, with first pedigerous somite incorporated into cephalothorax. Cephalothorax covered by minute scales (Fig. 6 C); cuticle with anastomosing pattern near the rostrum (Fig. 19 E) and along margins (Figs 6 C, 18A–B); additional ornamentation consisting of sensilla and pores as illustrated in Figure 6 C; posterior margin smooth. Pedigerous somites with reticulation along posterior margins and ornamentation consisting of sensilla as illustrated in Figure 6 C; epimera of second to fourth pedigerous somites expanded posteriorly; posterior margins serrate.

Urosome (Figs 6 C, 7A–B, 18A–C) 5-segmented, comprising P5-bearing somite, genital double-somite, 2 free abdominal somites and anal somite. Urosomites with surface ornamentation consisting of sensilla and reticulation as shown in Figures 7 A–B; posterior margin serrate.

Genital double-somite (Figs 6 C, 7A–B, 18A–B) original segmentation indicated by transverse, serrate surface ridge with reticulation and sensilla dorsally, and hook-like projections laterally (Figs 19 B–F), completely fused ventrally; genital field (Fig. 7 C) with surface striations, copulatory pore located in median depression; gonopores covered by opercula derived from sixth legs and by anteriorly directed flap arising from somite wall; P6 bearing 2 naked setae.

Anal somite (Figs 6 C, 7A–B, 18A–C, 19D). Anal operculum with posterior border serrate; large anal opening flanked by rows of spinous processes laterally (Fig. 19 D); surface striated with ornamentation consisting of setules and pair of sensilla dorsally, and setules ventrally.

Caudal rami (Figs 6 C–D, 7A–B) elongated, 12.5X as long as maximum width, and with pore on middle of outer margin. Each ramus with 7 setae: seta I naked and inserted at proximal third, seta II pinnate and inserted at middle third; seta III subdistal, unconfirmed shape and size (missing in holotype); setae IV and V fused basally, unconfirmed shape and size of both setae (broken in holotype), both bases covered by membranous extension; seta VI minute and flattened, displaced ventrally; seta VII tri-articulate at base and pinnate.

Rostrum (Figs 7 D, 19E) fused to cephalic shield; subtriangular; apex concave with tube-pore; pair of sensilla and additional surface ornamentation as illustrated in Figure 7 D.

Antennule (Figs 8 A, 19A) 7-segmented, with surface ornamentation consisting of rows of small denticles as shown in Figure 8 A. Segment I enlarged distally; segment III longest, with aesthetasc fused basally to seta and set on distinct pedestal; segment VI missing 1 spine/seta on both sides of holotype, insertion area arrowed in Figure 8 A; segment VII with aesthetasc fused basally to pinnate seta. Armature formula: I-[1 pinnate], II-[4 pinnate + 3 pinnate spines], III-[1 + 4 pinnate + 3 pinnate spines + (1 + ae)], IV-[2 pinnate + 1 pinnate spine], V-[1 pinnate + 1 pinnate spine], VI-[1 pinnate + 1 element], V-[6 pinnate + (1 pinnate + ae)].

Antenna (Figs 8 B–C) 3-segmented, comprising coxa, allobasis, and 1-segmented endopod. Coxa (not illustrated) small, with no ornamentation. Basis and enp-1 fused, forming elongate allobasis, with rows of spinules along inner and outer margins, insertion area of exopod swollen and covered by minute tubercles, abexopodal seta pinnate. Free endopod about half the length of allobasis; ornamented with long spinules along outer margin, and row of minute spinules along distal corner; medial armature consisting of 2 setae (1 naked and 1 pinnate) and 1 spine; apical armature consisting of 4 spines and 3 setae (1 naked and 2 pinnate), the shortest seta subdistal (Fig. 8 C). Exopod 4-segmented; with ornamentation as shown in Figure 8 B; exp-1 as long as next 3 segments combined; armature formula: I-[2 pinnate], II-[1 pinnate], III-[1 pinnate], IV-[2 pinnate].

Mandible (Fig. 8 D). Coxa with well developed gnathobase bearing several multicuspidate teeth and 1 pinnate seta around distal margin. Palp well developed, comprising basis, endopod and exopod. Basis with rows of spinules along inner, outer and distal margins, and 4 pinnate setae. Endopod 1-segmented, medial armature consisting of 3 naked setae; apical armature consisting of 7 setae (6 naked and 1 pinnate). Exopod 3-segmented; armature formula: I-[2 pinnate], II-[1 pinnate], III-[3 pinnate].

Maxillule (Fig. 9 A). Praecoxa with transverse fold and rows of spinules as shown in Figure 9 A; arthrite well developed, with 2 pinnate setae on anterior surface, with 7 spines (3 pinnate and 4 striated) and 3 setae (2 pinnate and 1 naked) along distal margin, posterior surface with patches of spinules and 2 naked setae. Coxa with row of spinules along distal margin of posterior surface; endite cylindrical, bearing 6 setae (2 pinnate and 4 naked) distally; epipodite represented by 1 missing element (insertion area arrowed in Figure 9 A). Basis and endopod fused; ornamentation consisting of rows of spinules on posterior surface; basis with 11 setae (1 pinnate and 10 naked); endopod incorporated into basis, represented by 3 naked setae. Exopod 1-segmented, with 3 pinnate setae.

Maxilla (Fig. 9 B) comprising syncoxa, allobasis and 3-segmented endopod. Syncoxa with 4 endites; proximal praecoxal endite cylindrical, ornamented with setules, and with 4 pinnate setae; distal praecoxal endite almost completely incorporated into syncoxa, with 3 setae (1 pinnate and 2 naked); proximal coxal endite with 3 naked setae; distal coxal endite with 2 naked setae and 1 naked spine; rows of spinules and setules along outer margin and additional ornamentation as shown in Figure 9 B. Allobasis endite forming strong claw; accessory armature consisting of 2 naked setae and 1 pinnate spine; endopodal armature of maxillar allobasis represented by 1 seta and 1 spine. Endopod with armature formula: I-[1 + 1 geniculate], II-[2 geniculate], III-[3 + 1 geniculate].

Maxilliped (Fig. 9 C) with elongated protopod and 2-segmented endopod. Protopod with rows of long setules along outer and inner margins; syncoxal endites represented proximal to distal by 1 pinnate seta and 1 pinnate spine, 2 pinnate setae and 1 pinnate spine, and 1 pinnate seta and 1 pinnate spine; basal endite represented by 1 pinnate seta and 1 pinnate spine. Endopod with armature formula: I-[1 pinnate], II-[2 pinnate spines + 2 pinnate setae].

P1 (Figs 9 D, 18C, 19C) biramous. Intercoxal sclerite well developed (Fig. 18 C), and with reticulated surface. Praecoxa with row of spinules along distal margin. Coxa with rows of spinules on anterior surface. Basis with 1 pinnate seta on inner corner and 1 pinnate seta on outer distal corner; ornamentation consisting of pore and patches of setules on anterior surface, and rows of spinules along outer margins. Exopod 1-segmented; with rows of setules along outer margin, and rows of minute spinules around bases of outer and apical setae; 5 pinnate setae along outer margin, 2 pinnate setae apically, and 2 pinnate setae along inner margin. Endopod 1-segmented, half length of exopod; ornamented with patches of spinules on anterior surface, and with rows of setules along outer margin; 1 pinnate seta along inner margin, 2 pinnate setae apically, and 1 pinnate seta on distal outer corner (outer and apical elements missing on both sides of holotype for drawing, but present during confocal imaging, insertion areas arrowed in Figure 9 D).

P2–P3 (Figs 10 A–C, 18C, 19F) biramous. Intercoxal sclerite well developed (cordiform in P2 and subrectangular in P3), with reticulated surface and row of setules along distal margin. Praecoxa well developed. Coxa with rows of minute spinules and setules on anterior surface, small spinules along distal margin, and long setules along outer margin. Basis with row of spinules along distal margin and rows of spinules on anterior surface, distal border with acute projection near endopod insertion, 1 pinnate seta on outer distal margin. Exopod-1 segmented; with row of setules along inner and outer margins (P3), anterior surface with patch of setules proximally and pore distally; outer and distal margins with acute projections. Endopod 2-segmented; enp-1 outer corner drawn out into bifid (P2) or blunt (P3) projection, with row of setules along outer (P2–P3) and distal (P2) margins; enp-2 outer margin with rows of setules and acute projections along outer (P2) and distal (P2–P3) margins. P2 enp-2 3X as long as enp-1; P3 enp-2 elongated and 2.5X as long as enp-1.

P4 (Figs 10 D, 19B, F) biramous. Intercoxal sclerite rectangular and with row of setules along distal margin. Praecoxa well developed. Coxa slightly striated, with rows of minute spinules on anterior surface. Basis with rows of spinules along inner and outer margins, and spinules on anterior surface. Exopod 1-segmented; slightly striated, ornamented with rows of setules along inner and outer margins. Endopod 1-segmented; reduced to cylindrical pedestal, bearing 1 pinnate seta.

P1–P4 spine and seta formulae as follows:

P5 (Figs 10 E, 19B). Protopod fused to supporting somite and with 1 outer pinnate seta. Exopod slightly striated; with 2 outer elements (proximal outer element missing in holotype, insertion area arrowed in Figure 10 E) and 1 apical pinnate seta.

MALE. Unknown.

Variability. The P3 enp-2 displayed [120] on one side and [020] on the other side of the same specimen.

Etymology. The species name is derived from the Latin arcticus, referring to the Arctic provenance of the material.