Doropygus antarcticus Kim & Boxshall 2020, sp. nov.

Doropygusantarcticus sp. nov.

(Figs. 226, 227)

Type material. Holotype ♀ (dissected and mounted on a slide, MNHN-IU-2014-21315) from Cnemidocarpa pfefferi Michaelsen, 1898, Antarctic (66°11 Ś, 143°21 É), CEAMARC 62EV303 (Beam Trawl AAD), Terre Adélie, “Aurora Australis” (66°11’S, 143°21’E), depth 532-550 m, IPEV-AAD-MNHN coll., 04 January 2008.

Additionalmaterial. 1 copepodid V ♀ (dissected) from Cnemidocarpa drygalskii (Hartmeyer, 1911), Antarctic Stn 65EV322 (65°48 Ś, 143°04 É), depth 750- 788 m, 05 January 2008.

Etymology. This species is named after the geographic region where the type locality is located.

Descriptionoffemale. Body (Fig. 226A) narrow, 4.85 mmlong: prosome 3.92 mmlong, indistinctly segmented. Dorsal cephalic shield distinct; second and third pedigerous somites each with weakly developed epimera. Fourth pedigerous somite forming elongated, oval brood pouch (about 1.5 times longerthan wide in lateral view). Freeurosome (Fig. 226B) slender, inserted anteriorly on brood pouch. Genital somite 215×449 μm, twice as wide as long; 4 freeabdominal somites 431×369, 412×345, 252×308, and 234×283 μm, respectively. Caudalramus (Fig. 226C) slender, graduallynarrowing distally, about 7.0 times longerthan wide (596×85 μm) and about 2.5 times longer than anal somite: armed with 6 small setae; outer proximal and dorsal setae positioned at 23% and 66% of ramus length, respectively; setae at most as long as width of ramus at base.

Rostrum (Fig. 226D) tapering towards rounded apex. Antennule (Fig. 226E) narrow, 660 μmlong, and 9- segmented; proximal 2 segments only slightly widerthan thirdsegment; armatureformula 3, 17, 6, 4+aesthetasc, 4, 3+aesthetasc, 2, 2+aesthetasc, and 7+aesthetasc; larger setae on first to fifth segments typically pinnate. Antenna (Fig. 226F) consistingof coxa, basis, and 2-segmented endopod; coxa shortand unarmed; basis 192×67 μm with 2 small (exopodal) setae at outer distal corner and 1 small inner seta distally; first endopodal segment 121×79 μm, unarmed, with convex outer margin; compound distal endopodal segment 4.1 times longer than wide (196×48 μm), armed with 10 small setae plus slender terminal claw.

Labrum (Fig. 226G) with slightly concave posterior margin bearing tufts of setules on either side of small setulose posteromedian lobe. Mandible (Fig. 226H) comprising coxa and palp; coxa with 5 teeth on cutting margin of gnathobase: basis with 1 setaon medial margin; exopod 4-segmented, with 1, 1, 1, and 2 setaeonfirst to fourth segments, respectively, outer seta on distal segment shorter (about 0.6 times as long as other 4 setae): endopod 2-segmented and incompletely articulated from basis, armed with 4 setae on first segment and 10 setae on second: all setae on mandible pinnate. Maxillule (Fig. 226I) with 9 setae on arthrite; coxal endite with 1 seta, epipodite with 1 small and 1 long seta: basis with 3 setae on medial margin, proximal seta shorter than distal 2; exopod with 3 setae and 1 small papilliform knob tipped with 1 thin setule between bases of first and second outer setae; endopod narrower than exopod, armedwith 3 setae. Maxilla (Fig. 227A) 5-segmented: syncoxawith 3 (plus 1 minute vestigial seta), 1, 2, and 3 setae on first to fourth endites, respectively: basis with strong claw bearing spinules distally on concave margin plus 2 unequal setae; endopod with 1, 1, and 4 setae on first to third segments, respectively. Maxilliped (Fig. 227B) incompletely 2- segmented: first segment armed with 9 setae on medial margin and ornamented with several rows on minute spinules on outer surface; second segment small, narrow, armed with 2 equal apical setae.

Leg 1 with both rami 3-segmented (Fig. 227C): lacking outer seta on basis; inner distal spine on basis 98 μm long, extending beyond distalborder offirst endopodal segment.

Legs 2–4with 3-segmentedexopods and 2-segmented endopods (Fig. 227D, E); exopods slightly longerthan endopods; outer setaon basis rudimentary; outer setae on exopods long and naked; distal setae of exopods and endopods naked. First exopodal segment about twice as long as wide inlegs 2 and 3, and 2.4 timeslongerthan wide in leg 4. Third exopodal segment about twice as long as wide in legs 2 and 3, and 2.9 times longer than wide in leg 4. Second endopodal segment of legs 2–4 slender, 4 times longer than wide and 2.6 times longer than first endopodal segment in legs 2 and 3, and 5.4 timeslongerthan wide and 3.2 times longer than first endopodal segment in leg 4. Armature formula for legs 1–4 as follows:

Leg 5 (Fig. 227F) consistingof protopod fused with somite, with small, naked seta on outer margin and row of fine spinules at inner distal corner, and slender free exopodal segment, 4.3 times longer than wide (239×56 μm), armed with 2 naked setae distally, inner less than half as long as outer; segment ornamented with 6 oblique rows of spinules on dorsomedial surface.

Male. Unknown.

Remarks. The exopod of the maxillule of D. antarcticus sp. nov. is characterised by having 3 setae plus a setule-tipped knob, which is probably the vestige of a seta. Asimilar exopodal armature has been recorded for two other species, D. demissus Aurivillius, 1885 and D. profundus Illg, 1958. According to Illg (1958), the setation of the maxillulary exopod of D. demissus can vary between three states: 3 setae, 3 setae plus a vestigial seta, or 4 well-developed setae. Unlike D. demissus, both D. antarcticus sp. nov. and D. profundus seem to consistently exhibit the characteristic armature of the maxillulary exopod, as did the copepodid Vjuvenile of D. antarcticus sp. nov.

Doropygusantarcticus sp.nov. iseasilydistinguishable from these two congeners by the proportional length of the caudal ramus. In D. antarcticus sp. nov. the caudal ramus is about 7.0 times longer than wide and about 2.5 timeslongerthan the anal somite, compared to 5 and 4.5 timeslongerthan wide in D. demissus and D. profundus, respectively, as described by Illg (1958) and less than twice as long as the anal somite, as figured by Illg (1958) for the latter two species.