Doropygus rectiuncinatus, 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 : 376-379

Doropygus rectiuncinatus sp. nov.

( Figs. 249 , 250 )

Type material. Holotype ♀ (dissected and mounted on a slide, MNHN-IU-2014-21326 ) from Polycarpa pedunculata Heller, 1878 (MNHN-IT-2008-6623 = MNHN S1/POL.B/417), Île des Pins, New Caledonia, Laboute coll., 1989.

Etymology. The specific name is derived from the Latin rect (=straight) and uncinat (=hooked) and alludes to the almost straight terminal claw of the antenna.

Descriptionoffemale. Body ( Fig. 249A ) narrow; 3.30 mmin length; prosome 2.31 mmlong.Dorsalcephalic shieldwell-defined.Metasomeincompletely4-segmented. Fourthpedigerous somite forming brood pouch, 1.3 times longer than wide in lateral view, with rounded posterior margin. Freeurosome ( Fig. 249B ) 5-segmented, slender, and cylindrical: genitalsomite 159×360μm; 4 abdominal somites 250×273, 250×236, 186×205, and 114×195 μm, respectively. Anal somite narrowing posteriorly, with deep posteromedian incision. Caudal rami parallel, not divergent ( Fig. 249C ), about 5.1 times longer than wide (327×64 μm) and gradually narrowing distally: armed with 6 small setae; all setae shorter than width of ramus at base; 2 proximal setae rudimentary, positioned at 28 and 65% of ramus length.

Rostrum ( Fig. 249D ) short, semicircular. Antennule ( Fig. 249E ) 360 μmlong, 9-segmented; 3 articulations between second to fifth segments indistinct; first and second segments broad; armatureformula 3, 14, 3, 4, 4, 3, 2, 2+aesthetasc, and 7+aesthetasc; setae generally very small, except 2 on first segment and 2 on sixth segment (one of setae on sixth segment pinnate); all other setae naked. Antenna ( Fig. 249F ) slender, 4-segmented; coxa shortand unarmed; basis unarmed, 145×47 μm, about 3 times longer than wide; first endopodal segment also unarmed, 93×42 μm, 2.2 timeslongerthan wide; compound distal endopodal segment 140×36 μm, 3.9 timeslongerthan wide; armedwith 6 smallsetae (distal 3 setae slightly unequal in length and positioned at base of terminal claw) plus relatively large, almost straight, terminal claw ( Fig. 249G ), 102 μm long, 0.73 times as long as segment, with membranous hyaline fringe along concave margin and around tip.

Labrum ( Fig. 249H ) bearing short, smooth posteromedian lobe; posterior margin with tuft of setules on each side. Mandible ( Fig. 249I ) with 5 teeth, 2 small proximal setae on coxal gnathobase, and 1 small subsidiary denticle between proximal second and third teeth: basiswith 1 seta mediodistally; exopodwith 4 large setae of equal length; endopod with 4 and 8 setae on first and second segments, respectively; 4 distal setae on second endopodal segment subequal in length. Paragnath not examined. Maxillule ( Fig. 249J ) armed with 9 setae on arthrite, 1 on coxal endite, 2 on epipodite, 3 on basis, 4 on exopod and 2 on endopod; setaon coxal endite attenuated, more than twice as long as wide; 3 medial setae on exopod increasing in length from outer to medial, all less than half length of larger outermost seta. Maxilla ( Fig. 249K ) with 3 (not 2) setae on fourth endite of syncoxa, otherwise as in D. humilis , D. parahumilis sp. nov., and D. breviuncinatus sp. nov. Maxilliped ( Fig. 250A ) incompletely 2-segmented, armedwith 9 setaeon first segment and 2 on second.

Leg 1 ( Fig. 250B ) with 3-segmented rami. Inner coxal seta extending to distal border of second endopodal segment. Outer seta on basis evenly attenuated. Inner distal spine on basis slender, 49 μm long, extending just to distal border of first endopodal segment, with minute spinules along margins. Legs 2–4 with 3-segmented exopods and 2-segmented endopods ( Fig. 250C, D ); basis lacking outer seta; third exopodal segment wider than long. Setae on second and third exopodal segments and distal setae on second endopodal segment unilaterally pinnate along proximal half of outer margin and finely spinulose distally. Armature formula for legs 1–4 as in D. breviuncinatus sp. nov.

Leg 5 ( Fig. 250E ) protopod with 1 rudimentary seta on outer margin and row of minute spinules at mediodistal corner: free exopodal segment about 3.0 times longer than wide (131×44 μm), armed distally with 2 unequal setae (82 and 38 μm, respectively), ornamented with 3 rows on minute spinules on dorsomedial surface.

Male. Unknown.

Remarks. This is the fourth species of Doropygus known to have a membranous hyaline fringe along the terminal claw of the antenna, as also found in D. humilis , D. parahumilis sp. nov. and D. breviuncinatus sp. nov. Unlike the latter three species, D. rectiuncinatus sp. nov. has a nearly straight terminal claw on the antenna, which is also relatively longer (102 μm), 0.73 times as long as the compounddistalendopodal segment. In comparison, the next longest terminal claw is found in D. humilis , which is 75 μm long but only 0.55 times as long as the segment. Other differences include; the setae on the antennule of D. rectiuncinatus sp. nov. are markedly smaller than those of the otherthree species, andthe fourthenditeof the maxillary syncoxa bears 3 setaerather than only 2 (the small proximal seta is lost in the other three species). The main differences between these four species are listed in Table 9 .

Figures

FIGURE 249. Doropygus rectiuncinatus sp. nov., female. A, habitus, right; B, urosome, ventral; C, right caudal ramus, dorsal; D, rostrum; E, antennule; F, antenna; G, distal part of antenna; H, labrum; I, mandible; J, maxillule; K, maxilla. Scale bars: A, 0.5 mm; B, 0.2 mm; C, 0.1 mm; D, 0.02 mm; E–K, 0.05 mm.

FIGURE 250. Doropygus rectiuncinatus sp. nov., female. A, maxilliped; B, leg 1; C, leg 2; D, leg 4; E, leg 5. Scale bars: A, 0.05 mm; B–E, 0.1 mm.