Notodelphyopsis gemina Kim & Boxshall 2020, sp. nov.

Notodelphyopsis gemina sp. nov.

(Figs. 55–57)

Typematerial. Holotype (intact ♀, MNHN-IU-2009- 5191), paratypes (19 intact ♀♀, MNHN-IU-2014-21232), and dissected paratypes (1 ♀, 1 ♂, figured), from Corella antarctica Sluiter, 1905, Antarctic Ocean (61°26 Ś, 41°55.4 Ẃ), depth 604 m, Eltanin cruise 12, 12 April 1964.

Etymology. The specific name is derived from the Latin gemin (=twin), alluding to the close similarity of the new species to Notodelphyopsis illgi.

Descriptionoffemale. Body (Fig. 55A) slender, 1.87 mm long. Cephalosome well-defined, but articulations between pedigeroussomites indistinct: first to third pedigerous somites lacking epimera. Brood pouch variable in form; fifth pedigerous somite completely fused to brood pouch. Free urosome (Fig. 55B) slender, 4-segmented. Genital double-somite (Fig. 55C) 210×149 μm, subdivided dorsally and ventrally by faint, indistinct suture line at anterior third and ornamented with several transverse rows of minute spinules on ventral surface. Three freeabdominal somites 152×131, 135×108, and 115×108 μm, respectively. Caudalramus (Fig. 55D) elongate, about 9.3 times as long as wide (325×35 μm) and 2.8 timeslongerthan anal somite, subdivided by constriction at 60% of length; ornamented with dense covering of setules on ventral surface; armed with 6 setae, 4 distal setae pinnate, other 2 naked, outer lateral seta located at 65% of ramus length.

[table omitted]

Rostrum (Fig. 55E) 87×70 μm, spatulate, with nearly parallel lateral margins. Antennule (Fig. 55F) slender, elongate, 575 μm long and extending to posterior margin of second pedigerous somite; 9-segmented (Fig. 30), armatureformula 3, 17, 6, 4+aesthetasc, 4, 2, 2, 2+aesthetasc, and 7+aesthetasc; several setae on proximal segments weakly pinnate, others naked (as figured). Antenna (Fig. 56A) 4-segmented, consistingof coxa, basis and 2-segmented endopod; coxa short and unarmed; basis with 2 equal, large pinnate setae representing exopod; first endopodal segment with 1 setaon inner margin; compound distal endopodal segment about 4.5 times longer than wide, armed with terminal claw and 11 setae and ornamented with 3 rows of spinules on distal half of outer side; 2 subdistal setae pinnate, others naked; 3 teminal setae blunt at tip; terminal claw small, about one-thirdaslongas segment.

Labrum (Fig. 55G) with deeply concave, setulose posterior margin. Mandible (Fig. 55H) consisting coxa and biramous palp: coxa with 4 teeth and 1 small seta on gnathobase; distalmost tooth acutely pointed: palp consisting of basis, exopod and 2-segmented endopod; basis with 1 seta and setules on medial margin; exopod 3-segmented, armed with 1, 2, and 2 setae on first to third segments, respectively, 2 distal setae much longerthan other 3; endopod incompletely articulated from basis, with 2 and 10 setaeon first and second segments, respectively, one seta on second segment smalland positionedon dorsal surface. Paragnath (Fig. 55I) as lobe bearing semicircular lobule at outer distal corner and setules on medial margin. Maxillule (Fig. 55J) with 9 setae (including 2 small) on arthrite, 1 on coxal endite, 2 on epipodite, and 3 on medial margin of basis (proximal seta much smaller than distal 2); exopod with 4 setae distally; endopod incompletely 2-segmented with 2 setae medially on first segment and 4 long, proximally-pinnate setaeon second segment. Maxilla (Fig. 56B) 5-segmented; syncoxawith 3+1 small, 1, 2, and 3 setae on first to fourth endites; basis with claw bearing spinules along concave margin, plus 2 setae; endopod with 1, 1, and 3 setae on first to third segments, respectively. Maxilliped (Fig. 56C) 3-segmented and armedwith 9 (2 spiniform), 0, and 3 setaeonfirst to third segments, respectively; second segment ornamented with setules along medial margin and patch of spinules distally.

Legs 1–4 with 3-segmented rami. Outer setaon basis of all swimming legs naked (Fig. 56 D–F). Inner distal spine on basis of leg 1 longer than first endopodal segment, 71 μm long. Armature formula for legs 1–4 as follows:

Leg 5 (Fig. 56G) reduced, represented by outer digitiform protopodal process tipped with naked seta and small free exopodal segment also tipped with naked seta.

Description of male. Body (Fig. 57A) tapering posteriorly and arched ventrally. Body length 785 μm. Cephalosome with well developed dorsal shield: second to fourth pedigerous somites each with well-developed dorsal tergite. Urosome (Fig. 57B) 6-segmented, with free fifthpedigerous somite, genitalsomite 62×86 μm, with row of fine spinules on ventral surface of each genital operculum, and 4 freeabdominalsomites 77×73, 77×73, 69×60, and 51×54 μm, respectively. First abdominal somite ornamented with 3 transverse rows of spinules on ventral surface (Fig. 57B). Caudal ramus about 4.8 times longer than wide (72×15 μm); armed with 6 setae, proximal outer lateral seta positioned at middle of ramus.

Rostrum as in female. Antennule (Fig. 57C) 10- segmented, non geniculate; segmental fusion pattern I-II, III-XI, XII, XIII, XIV, XV-XVI, XVII, XVIII-XX, XXI-XXIII, XXIV-XXVIII: armatureformula 3, 17, 2, 2, 2, 4+aesthetasc, 1, 3, 2+aesthetasc, and 11+aesthetasc; secondsegment incompletely subdivided proximally with traces of 2 suture lines on posterior surface. Antenna as in female.

Labrum, paragnath, maxillule, and maxilla as in female. Mandible with 9 setae (rather than 10 as in female) on second endopodal segment. Maxilliped (Fig. 57D) armed with 7 setae (grouped as 3 and 4) on first segment; second segment with patch of spinules distally asin female. Legs 1–5 asin female.

Remarks. Marchenkov & Boxshall (2003) distinguished Notodelphyopsis illgi (Marchenkov & Boxshall, 2003) from related species by its slender body shape, elongate antennule, and the extremely elongate caudal rami of the female. Notodelphyopsis gemina sp. nov. shares theseand otherfeatures with N. illgi. The latter species was recorded from the ascidian Corynascidia herdmani Ritter, 1913 living at a depth of 508 m in the North Pacific, whereas N. gemina sp. nov. was found in the Antarctic. Although the two species were found on different hosts and in very different zoogeographic regions, they display very few morphological differences. We note the following differences: (1) the body length of N. illgi is 2.37 mm in the female and 1.25 mm in the male, compared to 1.87 mm in the female and 0.79 mm in the male of N. gemina sp. nov.; (2) the caudal ramus of the female of N. illgi is 4.4 times longer than the anal somite, whereas it is only about 2.8 times longer in N. gemina sp. nov.; and (3) the antennule of the female is 10-segmented in N. illgi, but 9-segmented in N. gemina sp. nov. These differences are sufficient to justify the establishment of a new species.