Doropygus tuberculatus Kim & Boxshall 2020, sp. nov.

Doropygus tuberculatus sp. nov.

(Figs. 214, 215)

Typematerial. Holotype (intact ♀, MNHN-IU-2014- 21306) and paratype (♀, dissected and mounted on a slide, MNHN-IU-2014-21307) from Molgula pedunculata (Herdman, 1881), CEAMARC/cruise, Terre Adelie, Antarctic (67°02 Ś, 140°00 É), depth 180-205 m, 30 December 2007.

Additionalmaterial. 1 ♀ (dissected) from Molgula hodgsoni Herdman, 1910, South Georgia Island, South Atlantic.

Etymology. The specific name refers to the presence of the tapering distal tubercle on the caudal ramus.

Description of female. Body (Fig. 214A) of nonovigerous adult slender, withsmall brood pouch. Body length 3.37 mm. Metasome 4-segmented with fifth pedigerous somite incorporated into brood pouch. Free urosome (Fig 214B) 5-segmented: genitalsomite short, 150×378 μm; 4 abdominalsomites 306×363, 299×340, 230×300, and 190×265 μm, respectively. Caudalramus (Fig. 214C) slender, 5.5 timeslongerthan wide (334×61 μm), graduallynarrowing distally; armedwith 6 small setae and tapering distal tubercle (arrowed in Fig. 214D); all setae shorter than width of ramus at base; 2 proximal setae positioned at 34 and 68% of ramus length.

Body of ovigerous adult 4.75 mm long, with expanded, ovoid brood pouch. Metasomal somites defined only by surface constrictions. Caudal ramus twice as long as anal somite and 6.2 times longerthan wide, armed with 6 setae and distal tubercle.

Rostrum (Fig. 214E) longerthanwide, narrowing towardsroundedapex.Antennule(Fig.214F)9-segmented, segments broader near base, graduallynarrowing distally; armatureformula 3, 17, 6, 4+aesthetasc, 4, 3+aesthetasc, 2, 2+aesthetasc, and 7+aesthetasc; all setae naked. Antenna (Fig. 214G) slender, 4-segmented; coxashortand unarmed; basis more than twice as long as wide, with 3 small setae, 2 at outer distalcorner (representing exopod) and 1 at innerdistal corner; first endopodal segment unarmed, 0.6 times as long as basis, with protruding outer margin; compound distal endopodal segment 4.3 times longerthanwide (149×35 μm); armedwith 9 smallsetae (distal 3 blunt at tip) plus slender terminal claw, less than half aslongas segment.

Labrum (Fig. 214H) with almost straight posterior margin bearing setules on both sides and small, setulose posteromedianlobe. Mandible (Fig. 214I) with 5 acute teeth on coxal gnathobase; basis with 1 seta onmedial margin; exopod with 5 setae, shorter distamost seta half as long as other 4; endopod with 4 and 10 setae on first and second segments, respectively. Paragnath (Fig. 215A) as simple lobe bearing setules on medial margin. Maxillule (Fig. 214J) with 9 setae on arthrite, 1 on coxal endite, 2 on epipodite, 3 on basis, 4 onexopodand 3 on endopod. Maxilla (Fig. 215B) 5-segmented; syncoxawith 3, 1, 2, and 3 setae on first to fourth endites, respectively; basis with slender claw (spinulose along distal half of concave margin) plus 2 setae; endopodwith 1, 1, and 4 setaeon firsttothird segments, respectively. Maxilliped (Fig. 215C) incompletely 2-segmented; first segment with 9 (4 proximal and 5 distal) setae medially; short second segment with 2 setae apically.

Leg 1 (Fig. 215D) with 3-segmented rami; outer seta absent on basis; innerdistal spine on basis broad, spinulose and 73 μm long, extending to middle of second endopodal segment; outer spines on exopod fringed with narrow membranes. Legs 2–4 with 3-segmented exopods and 2-segmented endopods (Fig. 215E, F); outer seta on basis vestigial; exopod bearing setae only. Armature formula for legs 1–4 as follows:

Leg 5 (Fig. 215G) 2-segmented: protopod broad, unornamented, but armed with small, naked seta at outer distal corner; free exopodal segment gradually narrowing distally, 2.8 times longer than wide (164×58 μm), ornamented with 5 rows of fine spinules on dorsomedial surface, and armed with 2 naked distal setae, inner shorter than outer.

Male. Unknown.

Remarks. Doropygus tuberculatus sp. nov. closely resembles D. kerguelensis (redescribed above). Both species may be found in the same ascidian host, Molgula pedunculata at localities around Antarctica. Doropygus tuberculatus sp. nov. can be distinguished from D. kerguelensis by the presence of a distal tubercle on the caudal ramus (this tubercle is absent in D. kerguelensis), the armature of 1 claw plus 2 setae on the basis of the maxilla (3 setae in D. kerguelensis), by having naked setae on the antennule (most of the large setae are pinnate in D. kerguelensis), and by the presence of 5 spinule rows on the exopod of leg 5 (only 4 spinule rows in D. kerguelensis). These consistent differences support the establishment of the new species.