Thoracodelphys papuensis, 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 : 438-441

Thoracodelphys papuensis sp. nov.

( Figs. 290 , 291 )

Type material. Holotype ♀ (dissected and mounted on a slide, MNHN-IU-2014-21354 ) from Botryllusperspicuum Herdman, 1886 , CRRFCRCHO 500, Fringing Reef, Cape Pievost, Papua New Guinea (10°06.43 Ś, 150°57.84 É), 20 January 2002.

Etymology. The species is named after its type locality, Papua New Guinea.

Description of female. Body ( Fig. 290A ) dorsoventrally depressed, 1.24 mm long. Prosome taperinganteriorly, 0.89 mm long. Dorsalcephalic shield with poorly defined posterior margin: metasome with 3 dorsal constrictions defining 4 pedigerous somites; brood pouch extending through second to fourth pedigerous somites and containing eggs. Free urosome ( Fig. 290B ) 5-segmented; genital and 4 abdominal somites 54×140, 77×112, 65×102, 63×90, and 58×80 μm, respectively. Anal somite with broad posteromedian incision and parallel lateral margins. Caudal rami widely separated from each other; each ramus ( Fig. 290C ) 5.2 times longer than wide (104×20 μm) and with nearly parallel lateral margins: armedwith 2 setae (outer proximal and dorsal) and 4 distal spines; outer proximal and dorsal setaelocated at 28 and 60% of ramus length, respectively, both setae longer than width of ramus at base; 4 distal spines slender and all shorter than width of ramus at base, longest spine 17 μmlong.

Rostrum small withroundeddistal margin.Antennule ( Fig. 290D ) small, 120 μmlong, taperingdistally, 6- segmented; armatureformula 3, 14, 6+aesthetasc, 4+aesthetasc, 3+aesthetasc, and 7+aesthetasc; setae very crowded, all naked; 2 larger setae on first segment equal and about as long as entire antennule.Antenna ( Fig. 290E ) 4-segmented; coxa unarmed; basis with 2 minute setal vestiges at outer distal corner representing exopod; first endopodal segment unarmed, slightly longer than basis; compound distal endopodal segment about 3.8 times longerthan wide: armedwith 8 setae (arranged as 3, 2, and 3) plus terminal claw half as long as segment.

Labrum ( Fig. 291A ) smooth with large, semicircular posteromedian lobe and convex posterior margin. Mandible ( Fig. 290F ) with 5 teeth and 1 small setaon coxal gnathobase; distalmost tooth acutely pointed, with minutespinulesalongproximal margin: basiswith 1 seta subdistally on medial margin; exopod armed with 5 setae (distal 3 distinctly shorter than proximal 2); endopod armed with 2 and 5 setae on first and second segments, respectively.Maxillule ( Fig. 290G ) with 8 setaeon arthrite, 1 on coxal endite, 2 on epipodite, 3 on basis (proximal seta about one-third as long as distal 2); 3 on exopod and 2 on endopod. Maxilla ( Fig. 290H ) segmented and armed asin T. caledonica sp. nov. Maxilliped ( Fig. 291B ) armed with 7 medial and 1 outer subdistal setae.

Legs 1–4 ( Fig. 291 C-F) with 3-segmented exopods and 2-segmented endopods; innercoxalsetaabsent. Inner distal spine on basis of leg 1 extending beyond distal border of first endopodal segment, 31 μm long, spinulose in distal half. First exopodal segment of legs 2–4 with large, pointed anterodistal process bearing small subsidiary denticle subdistally. Second exopodal segment of legs 2–4 with large, bifurcate anterodistal process. First exopodal segments of legs 3 and 4 lacking outer element, but bearing inner seta. Armature formula for legs 1–4 as follows:

	Coxa	Basis	Exopod	Endopod
Leg 1	0-0	1-I	I-1; 1-1; 3, 1, 4	0-0; 1, 2, 3
Leg 2	0-0	1-0	1-1; 1-1; 2, 1, 5	0-1; 1, 2, 5
Leg 3	0-0	1-0	0-1; 1-1; 2, 1, 5	0-1; 1, 2, 5
Leg 4	0-0	1-0	0-1; 1-0; 2, 1, 5	0-0; 1, 2, 1

Leg 5 ( Fig. 291G ) small, represented by 1 lateral seta on ventrodistal surface of somite and free exopod segment 12×18 μm, narrowing distally, armed with inner spine (16 μm long) and outer seta (35 μm long).

Male. Unknown.

Remarks. Thoracodelphys papuensis sp. nov. has a 6-segmented antennule and 8 setae on the third exopodal segment of leg 2. The combination of these two features is shared by only two other species in the genus, T. chelipus and T. uniseta . Thoracodelphys papuensis sp. nov. can be readily distinguished from these two species because its maxilliped is armed with 8 (7+1) setae, in contrast to the 7 (6+1) setae exhibited by T. chelipus and T. uniseta . The setation of the first exopodal segments of legs 3 and 4 (which lack an outer seta but bear an inner seta; armatureformula 0-1) of T. papuensis sp. nov. is unique within the genus. Other congeneric species have an armature formula for the first exopodal segment ranging from 1-0 to 1-1 or I- 1 in leg 3, and 1-0 or I-0 to 0-0 inleg 4.

Figures

FIGURE 290. Thoracodelphys papuensis sp. nov., female. A, habitus, right; B, urosome, ventral; C, right caudal ramus, ventral; D, antennule; E, antenna; F, mandible; G, maxillule; H, maxilla. Scale bars: A, 0.2 mm; B, 0.05 mm; C–H, 0.02 mm.

FIGURE 291. Thoracodelphys papuensis sp. nov., female. A, labrum; B, maxilliped; C, leg 1; D, leg 2; E, leg 3; F, leg 4; G, leg 5. Scale bars: 0.02 mm.