Doropygus rotundus, 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 : 350-353

Doropygus rotundus sp. nov.

( Figs. 232 , 233 )

Type material. Holotype ♀ (dissected and mounted on a slide, MNHN-IU-2015-9) from Pyura vittata (Stimpson, 1852) (MNHN-IT-2008-XXXX = MNHNS2 / PUY /495), GUYANE 2014 CP4348, French Guiana, N/O “ Hermano Gines ” (05°46’N, 51°23’W), depth 115 m, MNHN - convention APA-973-1 coll., 27 July 2014.

Etymology. The specific name is derived from the Latin rotund (=round) and refers to the rounded brood pouch.

Descriptionoffemale. Body ( Fig. 232A ) slightly compressed, 3.30 mm long. Dorsalcephalic shield welldefined posteriorly but pedigerous somites incompletely separated. Fourth pedigeroussomite forming stout brood pouch with rounded posterior margin. Free urosome 5- segmented. Caudalramus ( Fig. 232B ) stout, about 2.8 timeslongerthan wide (156×56 μm): armedwith 6 small, thin setae; 2 proximal setae positioned at 28 and 38% of ramus length, respectively; both inner and outer margins slightly convex; all setae shorter than maximum width of ramus.

Rostrum ( Fig. 232C ) widerthan long, sub-spatulate, narrowing distally towards broadly rounded apex. Antennule ( Fig. 232D ) 9-segmented; first and second segmentsdistinctly broaderthan distal segments; armature formula 3, 16+spine, 6, 4+aesthetasc, 4, 2+aesthetasc, 3, 2+aesthetasc, and 7+aesthetasc; 2 pinnate setaeon each of first and fourth segments and 1 each on second, third, fifth and sixth segments; all other setae naked. Antenna ( Fig. 232E ) slender and 4-segmented; coxa unarmed; basis with 3 small setae, 2 on tip of small subdistal knob (representing exopod) plus setaon distal border; first endopodal segment unarmed with protuberant outer margin; compound distal endopodal segment elongate, about 5.2 timeslongerthan wide (136×26 μm); armed with 7 small setae plus small terminal claw, less than half length of segment.

Labrum ( Fig. 232F ) and paragnath ( Fig. 232H ) as in D. elongatus sp. nov. Mandible ( Fig. 232G ) with 5 teeth on coxal gnathobase, distalmost tooth bearing minute spinulesalong proximal magin; basiswith 1 seta onmedial margin; exopod unsegmented with 5 setae (distalmost seta about 0.7 times as long as other 4 setae); first endopodal segment fused with basis, with 4 setae medially and row of minute spinules at outer distal corner; second endopodal segment armed with 9 setae (second outerdistalseta longest), and ornamented with fine spinules at outer and innerdistal corners. Maxillule ( Fig. 232I ) and maxilla ( Fig. 232J ) armed as in D. elongatus sp. nov. Maxilliped ( Fig. 233A ) 2-segmented; first segment with 8 setae on medial margin; second segment small, with 2 equal setae distally.

Leg 1 ( Fig. 233B ) biramous with 3-segmented rami. Outer seta on basis broad proximally and flagellate distally. Inner distal spine on basis 68 μm long, extending to middle of second endopodal segment. Legs 2–4 ( Fig. 233 C-E) with 3-segmented exopods and 2-segmented endopods. Inner coxal seta well-developed, more than twice as long as entire endopod. Outer seta on basis small and naked. Exopod as long as endopod in leg 2, slightly longer in leg 3, and 1.4 times longer in leg 4. Armature formula for legs 1–4 as in D. martiniquensis sp. nov.

Leg 5 ( Fig. 233F ) 2-segmented: protopod widerthan long, not articulated at base, with small, naked seta at outer distal corner and patch of spinules on inner surface; free exopodal segment gradually narrowing distally, about 3.1 times longerthan wide (125×41 μm), armed distally with inner and outer setae (longer outer seta about 5 times longerthan inner seta), ornamented with 4 rows of fine spinules on dorsomedial surface.

Male. Unknown.

Remarks. The three new species, D. martiniquensis sp. nov., D. elongatus sp. nov. and D. rotundus sp. nov. described above, are all associated with ascidians of the genus Pyura in the tropical West Atlantic. These three are very alike in terms of the morphology of their cephalic appendages and all three have the same armature formula for the legs. In addition, they also share two unusual features: firstly, the first segment of the maxilliped bears 8 setae (not 9 as usual), and secondly, the first exopodal segment lacks an inner seta in legs 3 and 4. Interestingly, these three species are easily distinguishable from one another without dissection by the characteristic form of the brood pouch, i.e., which is distally conical in D. martiniquensis sp. nov., elongate and posteriorly truncate in D. elongatus sp. nov., and stout and roundedposteriorly in D. rotundus sp. nov. In addition, the length of the inner coxal seta on leg 1 is a reliable character to use to differentiate between them: it is about 1.5 times longer than the endopod in D. martiniquensis sp. nov., as long as the endopod in D. elongatus sp. nov., and more than twice as long as the endopod in D. rotundus sp. nov. The relative length and shape of the caudal ramus, the second endopodal segment of the antenna, and the exopod of leg 5 also exhibit differences (as summarised in Table 8 ).

Group C (maxillule with 4 setae on exopod and 2 setaeon endopod)

Figures

FIGURE 232. Doropygus rotundus sp. nov., female. A, habitus, right; B, left caudal ramus, dorsal; C, rostrum; D, antennule; E, antenna; F, labrum; G, mandible; H, paragnath; I, maxillule; J, maxilla. Scale bars: A, 0.5 mm; B–J, 0.05 mm.

FIGURE 233. Doropygus rotundus sp. nov., female. A, maxilliped; B, leg 1; C, leg 2; D, leg 3; E, leg 4; F, leg 5. Scale bars: A, F, 0.05 mm; B–E, 0.1 mm.