Doropygus gracilis, Kim & Boxshall, 2020

Kim, Il-Hoi & Boxshall, Geoff A., 2020, Untold diversity: the astonishing species richness of the Notodelphyidae (Copepoda: Cyclopoida), a family of symbiotic copepods associated with ascidians (Tunicata), Megataxa 4 (1), pp. 1-6 : 336

Doropygus gracilis sp. nov.

( Figs. 222 , 223 )

Type material. Holotype ♀ (dissected and mounted on a slide, MNHN-IU-2014-21313) from Molguloides vitrea (Sluiter, 1904) (MNHN-IT-2008-5883 = MNHNS3/ MOL.B/36), KARUBAR Expedition, between Kai Island and Tanimbar, Indonesia, depth 350 m, 21 October - 05 November 1991.

Etymology. The specific name is from the Latin gracil (=slender) and alludes to the slender body form of the new species.

Descriptionoffemale. Body ( Fig. 222A ) slender, 3.60 mmlong. Prosome 2.60 mmlong, slightlydepressed. Dorsal cephalic shield relatively small, well-defined. Metasome with 4 pedigerous somites delimited only by weak dorsal wrinkles. Fourth pedigerous somite forming brood pouch, much longer than wide. Free urosome 5- segmented. Caudalramus ( Fig. 222B ) elongate, about 9.1 timeslongerthan wide (444×49 μm) and about 1.7 timeslongerthan anal somite; armedwith 6 setae (outer proximal, dorsal, and 4 distal); setae small, all shorter than maximum width of ramus; outerproximal and dorsal setae positioned at 28 and 67% of ramus length, respectively.

Coxa Basis Exopod			Endopod
Leg 1 0-1 Legs 2 & 30-1 Leg 4 0-1	1-I 1-0 1-0	I-1; I-1; III, I, 4 1-1; 1-1; 3, 1, 5 1-0; 1-1; 2, 1, 5	0-1; 0-1; 1, 2, 3 0-1; 1, 2, 5 0-1; 1, 2, 4

Rostrum ( Fig. 222C ) 125×167 μm, triangular, with blunt apex. Antennule ( Fig. 222D ) 300 μm long, 9-segmented, tapering distally from broader proximal segments, curved; armatureformula 3, 16+aesthetasc, 5?, 3?, 3? 2, 2, 2, and 7+aesthetasc; setae crowded, generally long, many pinnate. Antenna ( Fig. 222E ) slender, 4- segmented; shortcoxa unarmed; basis 120×50 μm, bearing 1 small seta distally and 1 small papilliform knob (exopod) tipped with 1 large seta (137 μm long) and 1 minute seta; first endopodal segment 89×50 μm, with 1 small seta subdistally on inner margin; compound distal endopodal segment about 4.2 times longer than wide (131×31 μm); armed with 9 setae arranged as 1, 3, 2, and 3 (3 distal setae bluntly tipped), plus elongate terminal claw, 100 μm long and 0.76 times as long as segment.

Labrum( Fig.222F )withhemisphericalposteromedian lobe and ornamented with scattered setules on posterior margin. Mandible ( Fig. 222G ) with 5 pointed teeth and 2 smallsetae on coxal gnathobase: basis with 1 seta mediodistally; exopod 3-segmented, with 1, 1, and 3 setae on first to third segments, respectively; distalmost seta rudimentary, naked; other 4 setae large, subequalin length; endopod with 4 and 9 setaeon first and second segments, respectively. Paragnath ( Fig. 223A ) setulose onmedial surface; apex angular. Maxillule ( Fig. 222H ) armed with 9 setaeon arthrite, 1 on coxal endite, 2 on epipodite, 3 on medial margin of basis, 4 on exopod, and 3 on endopod. Maxilla ( Fig. 223B ) 5-segmented; syncoxawith 9 setae arranged as 3, 1, 2, and 3; basis with 3 setae; endopod with 1, 1, and 4 setae on first to third segments, respectively. Maxilliped ( Fig. 222I ) incompletely segmented; first segment armed with 9 setae (4 proximal and 5 distal) and ornamented with tuft of setules proximally; small second segment tipped with 2 setae and ornamented with setules onmedial margin.

Leg 1 ( Fig. 223C ) with 3-segmented rami. Inner distal spine on basis 61 μm long, extending beyond distal border of first endopodal segment; outer spines on exopod slender, that of first exopodal segment large, extending to base of second spine on third exopodal segment. Legs 2–4 with 3-segmented exopods and 2-segmented endopods ( Fig. 223D, E ). Inner seta on coxa well-developed, but outer setaon basis very small; outer setae on exopods and distal setae on endopods naked. Leg 4 lacking inner seta on first exopodal segment. Armature formula for legs 1–4 as follows:

Leg 5 ( Fig. 223F ) 2-segmented: protopod wider than long, not articulated at base, with 1 thin seta on outer margin and spinules on distal border; free exopodal segment about 3.3 timeslongerthan wide (140×43 μm), tapering in distal third, with 2 unequal setae distally (100 and 50 μm long, respectively) and 4 rows of minute spinules on dorsomedial surface.

Male. Unknown.

Remarks. As a striking feature of Doropygus gracilis sp. nov., the antenna bears a large seta on a small knob (representing the exopod) located at the outer distal angle of the basis. In the Notodelphyidae this feature is an attribute of some relatively primitive genera, such as the members of the Botachus -group (e.g. Goniodelphys and Periproctia ), and some species of Doropygopsis . In other respects, the new species conforms to the generic diagnosis of Doropygus . Thus, for example, the form and armature of the caudal ramus, maxilliped and leg 5, and the segmentation and armature of the swimming legs are all typical for Doropygus . In addition to the large seta on the basis of the antenna, the slender body, the elongate caudal ramus, and the small size of the distalmost seta on the mandibular exopod are features that serve to distinguish the new species from its congeners.

Figures

FIGURE 222. Doropygus gracilis sp. nov., female. A, habitus, right; B, right caudal ramus, ventral; C, rostrum; D, antennule; E, antenna; F, labrum; G, mandible; H, maxillule; I, maxilliped. Scale bars: A, 0.5 mm; B, C, 0.1 mm; D–I, 0.05 mm.

FIGURE 223. Doropygus gracilis sp. nov., female. A, paragnath; B, maxilla; C, leg 1; D, leg 2; E, leg 4; F, leg 5. Scale bars: A, B, F, 0.05 mm; C–E, 0.1 mm.