Doropygus leptobrachius, 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 : 364

Doropygus leptobrachius sp. nov.

( Figs. 241 , 242 )

Typematerial. Holotype (intact ♀, MNHN-IU-2014- 21322 ) , paratypes (22 intact ♀♀, MNHN-IU-2014- 21323), and dissected paratypes (3 ♀♀, figured) (most with caudal rami missing) from Microcosmus vulgaris Heller, 1877 (MNHN-IT-2008-5255 = MNHN S2/ MIC /31), trawl, Banyuls on Mediterranean coast of France, Monniot coll., 1961.

Additional material. 1 ♀ (MNHN-IU-2017- 2169) from M. vulgaris , Mediterranean (42°13.67 Ń, 09°37.43 É), MEDITS 2016 Stn M16-4, depth 109 m; 1 ♀ (MNHN-IU-2017-2173) from M. vulgaris , Mediterranean (41°50.74 Ń, 09°27.53 É), MEDITS 2016, Stn M16-3, depth 72 m.

Etymology. This species name is derived from the Greek lept (=slender) and brachi (=arm), and alludes to the slender antenna.

Descriptionoffemale. Body ( Fig. 241A ) rather stout, weakly bilaterally compressed; body length 3.10 mm. Prosome 2.50 mm long, distinctly segmented, consistingof cephalosome and 4 pedigerous somites. Fourthpedigerous somite forming brood pouch about 1.4 times longer than wide in lateral view, weakly tapering posteriorly. Free urosome 5-segmented, gradually narrowingposteriorly; genitalsomite 190×400 μm; 4 abdominal somites gradually shorter, 223×318, 200×277, 127×232, and 120×227 μm. Anal somite with shallow posteromedian incision. Caudalramus ( Fig. 241B ) about 3.8 times longer than wide (188×50 μm) and about 1.6 timeslongerthan anal somite; armedwith 6 small setae; 2 proximal setae positioned at 27 and 61% of ramus length.

Rostrum ( Fig. 241C ) longerthanwide, spatulate, with parallel lateral margins and broadly rounded apex. Antennule ( Fig. 241D ) 390 μm long, 9-segmented; articulations between 3 terminal segments indistinct; armatureformula 3, 17, 5, 4+aesthetasc, 3, 2+aesthetasc, and 7+aesthetasc; setae moderately long, all naked. Antenna ( Fig. 241E ) slender, 4-segmented; shortcoxa unarmed; basis 98×44 μm, with 1 seta distally and 1 tiny seta near outer distal corner; first endopodal segment 73×39 μm, with 1 smallseta subdistally; compound distal endopodal segment elongate, about 5.4 times longer than wide (130×24 μm); armed with 5 setae arranged as 1, 1, 2, and 1 (with distalmost seta more than half length of terminal claw) plus terminal claw 77 μm long, 0.59 times aslongas segment.

Labrum ( Fig. 241F ) with well-developed, linguiform posteromedian lobe ornamented with setules on both sides; posteriormargin setulose. Mandible ( Fig. 241G ) with 5 teeth and 2 small setae on coxal gnathobase; distalmost tooth sharply pointed, with minute spinules on proximal margin: basiswith 1 seta mediodistally; exopod 4-segmented with 4 equally large setae, 1 per segment; endopod distinctly articulated from basis, 2-segmented; first segment with 4 setae on medial margin and row of minute spinules on mediodistal border; second segment with 9 setae, second outer setaon distal margin longest, 1.2 times longer than second longest third seta. Paragnath ( Fig. 241H ), maxillule ( Fig. 241I ), maxilla ( Fig. 242A ), and maxilliped ( Fig. 242B ) as in D. pulex .

Leg 1 ( Fig. 242C ) biramous with 3-segmented rami. Outer seta on basis naked, abruptly thinning to flagellate tip. Inner distal spine on basis 67 μm long, extending beyond distal border of first endopodal segment. Legs 2–4 similar to those of D. pulex ( Fig. 242D, E ). Leg 5 ( Fig. 242F ) similar to that of D. pulex , but free exopodal segment shorter, 2.1 timeslongerthan wide (107×51 μm).

Male. Unknown.

Remarks. Illg & Dudley (1961) redescribed D. pulex based on specimens taken from Microcosmus sulcatus Coquebert, 1797 collected in the Mediterranean. This ascidian is now recognized as a synonym of M. vulgaris (WoRMS Editorial Board, 2020) . Thetype material of D. leptobrachius sp. nov. described above was collected from the same ascidian host species and in the same geographical region. However, our specimens exhibit two significant differences from the redescription of Illg & Dudley, even though the form of the rostrum and the distal armature of the antenna are the same as those of Illg & Dudley’s specimens. First, the caudal ramus of D. leptobrachius sp. nov. is 3.8 times longer than wide and about 1.6 times longer than anal somite, in contrast to 5.7 times longer than wide and 2.6 times longer than anal somite in Illg & Dudley’s specimens (as measured by Illg & Dudley, 1961). Second, in the antenna of D. leptobrachius sp. nov. the basis and the first and second endopodal segments are 98, 73, and 130 μm long, respectively, thus the second (compound distal) endopodal segment is markedly longer than the basis in contrast to theproportionallengths 6.7: 4.0: 5.6 in Illg & Dudley’s specimens where this segment is shorter than the basis. The slender form of the second endopodal segment of the antenna of D. leptobrachius sp. nov. was confirmed in all available specimens after dissection or without dissection. Other differences, such as the presence of 8 setae on the secondendopodal segment of the mandible in Illg & Dudley’s specimens, were not considered as part of the justification for establishing the new species because of possible variability.

Figures

FIGURE 241. Doropygus leptobrachius sp. nov., female. A, habitus, right; B, right caudal ramus, medial; C, rostrum; D, antennule; E, antenna; F, labrum; G, mandible; H, paragnath; I, maxillule. Scale bars: A, 0.5 mm; B–I, 0.05 mm.

FIGURE 242. Doropygus leptobrachius sp. nov., female. A, maxilla; B, maxilliped; 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.