Doropygus tenuicaudatus, 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 : 332-336

Doropygus tenuicaudatus sp. nov.

( Figs. 220, 221)

Typematerial. Holotype (intact ♀, MNHN-IU-2014- 21311) and paratype ♀ (dissected and mounted on a slide, MNHN-IU-2014-21312) from Herdmania mauritiana (Drasche, 1884) (MNHN-IT-2008-4578 = MNHNS 2/ HER /22), CRRFCRCHO 239, Malakal Harbor, Koror, Palau (07°19.88’N, 134°27.50’E), depth 1 m, 28 January 1998.

Etymology. The specific name combines the Latin words tenu (=slender) and cauda (=tail), alluding to the slender urosome of the new species.

Description of female. Body ( Fig. 220A) with thick, rigid exoskeleton; bodylength 4.57 mm. Prosome 5-segmented: cephalosome and first to third pedigerous somites dorsoventrally depressed. Dorsal cephalic shield and second and third pedigerous somites each with thickened lateral margins marked with surface granulation, acutely pointed posterolateral corners, and with fine serrations along posterodorsal margin ( Fig. 220B). Fourth pedigerous somite forming large brood pouch, morethan twiceas longas anterior partof prosome, characteristically strongly compressed, disc-shaped and rounded both dorsally and posteriorly in lateral view, with dorsal groove (indicated by arrowhead in Fig. 220A) along midline. Cephalicshield to third pedigerous somites with smooth dorsal surfaces, but external surface of brood pouch reticulated with polygonal sculpturing ( Fig. 220C). Freeurosome ( Fig. 220D) 5-segmented, extremely narrow; genital somite 154×241 μm, narrowing in posterior half. Four abdominal somites each longer than wide, 250×186, 273×168, 255×150, and 168×132 μm. Caudalramus ( Fig. 220D) thin, about 12 timeslongerthan wide (673×55 μm) and 4.0 timeslongerthan anal somite; armedwith 6 minute setae; outer proximal and dorsal setae located at 25 and 72% of ramus length, respectively.

Rostrum ( Fig. 220E) as short, broad anterior process on cephalosome. Antennule ( Fig. 220F) 327 μm long, 9- segmented; armatureformula 3, 16, 6, 4+aesthetasc, 4, 3+aesthetasc, 2, 2+aesthetasc, and 7+aesthetasc; setae crowded and mostly long, larger setae pinnate. Antenna ( Fig. 220G) slender, 4-segmented; coxashortand unarmed; basis about 3 times longer than wide, broad distally, armed with 2 small setae (1 outer distal and 1 inner distal); first endopodal segment about 1.6 times longer than wide, with 1 small seta subdistally on inner margin; compound distal endopodal segment elongate, about 5.6 times longer than wide (173×31 μm) and 2.3 timeslongerthan firstendopodal segment; armedwith 8 setae and few minute spinules, plus small terminal claw, less than one-third as long as segment.

Labrum ( Fig. 220H) with narrow, straight posterior margin bearing patch of minute setules on both sides and large, smoothposteromedian lobe. Mandible ( Fig. 220I) with 7 teeth, distalmost seta thin, acutely pointed, and 1 smallproximal seta; basis with 1 seta distally onmedial margin; exopod slender, with 5 setae, distalmost seta more slender and shorter than other 4; endopod with 4 and 9 setae on first and second segments, respectively; second endopodal segment ornamented with spinules on distal half of outer margin. Maxillule ( Fig. 221A) with 9 setae on arthrite, 1 broad seta on coxal endite; 2 on epipodite, 3 on basis (proximal seta markedly shorter than distal 2), 4 on exopod, and 3 on endopod. Maxilla ( Fig. 221B) 5-segmented; syncoxawith 9 setae (3, 1, 2, and 3); basiswith 3 setae; endopodwith 1, 1, and 4 setae on first to third segments, respectively. Maxilliped ( Fig. 221C) unsegmented, but with partial suture between broad proximal and short, narrow distal parts; armed with 9 setae medially and 2 setae apically.

Leg 1 ( Fig. 221D) with 3-segmented rami. Inner coxal seta plumose, extending to middle of third endopodal segment. Outer seta on basis digitiform basally and flagellate distally. Inner distal spine of basis stout, 42 μm long, spinulose along distal half. Distal spine on third exopodal segment elongated, about 1.7 times longer than segment.

Legs 2–4 ( Fig. 221 E-G) with 3-segmented exopods and 2-segmented endopods; both rami very slender and with endopods distinctly longer than exopods; first exopodal segment lacking inner seta. Inner coxal seta of legs 2 and 3 naked, short (not extending beyond distal border of first endopodal segment); inner coxal seta of leg 4 rudimentary, almost invisible. Outer seta on basis of legs 2–4 minute. Setaeon exopods elongate, mostly longer than ramus. Proximal inner seta on second endopodal segment of leg 3, proximal 3 setaeon endopod of leg 4, and inner seta on second exopodal segment of leg 4 rudimentary. Second endopodal segment as long as entire exopod in legs 2 and 3, and longer than entire exopod in leg 4. Armature formula for legs 1–4 as follows:

Coxa Basis Exopod Endopod

Leg 1 0-1 1-I I-1; I-1; III, I, 4 0-1; 0-1; 1, 2, 3 Leg 2 0-1 1-0 1-0; 1-1; 3, 2, 4 0-1; 1, 3, 4

Leg 3 0-1 1-0 1-0; 1-1; 2, 2, 4 0-1; 1, 3, 4

Leg 4 0-1 1-0 1-0; 1-1; 2, 2, 4 0-1; 1, 3, 3

Leg 5 ( Fig. 221H) 2-segmented: protopod short with 1 seta at outer distal corner and several spinules on distal border; free exopodal segment elongate, about 6.3 times longer than wide (125×20 μm), with parallel lateral margins, armed with 2 unequal setae distally, and ornamented with 3 rows of spinules on dorsomedial surface.

Male. Unknown.

Remarks. Doropygus tenuicaudatus sp. nov. has thick exoskeleton and the surface of the brood pouch is reticulated, as found in D. reticulatus sp. nov. and D. caribbensis sp. nov. It cannot be confused with either of these two species or with any other congeneric species, because of the extreme elongation of the caudal rami, which are about 12 times longer than wide. In comparison, the largest recorded length:width ratio of the caudal ramus in other species of Doropygus is 8: 1 in D. platythorax (see Jones, 1974). Other significant differences between D. tenuicaudatus sp. nov., D. reticulatus sp. nov., and D. caribbensis sp. nov. are summarised in Table 7.