Thoracodelphys longiseta, 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 : 427-432

Thoracodelphys longiseta sp. nov.

( Figs. 284 , 285 )

Type material. Holotype ♀ (dissected and mounted on a slide, MNHN-IU-2014-21349 ) from Botryllus sp., Port of Roi George (October 1829), Stn 90, Port Western , collected by the Australian research vessel, Astrolabe.

Etymology. The specific name refers to the two extremely long setae on the first segment of the female antennule.

Descriptionoffemale. Body ( Fig. 284A ) slightly depressed and moderately inflated: body length 1.40 mm. Prosome 1.02 mmlong, taperinganteriorly, with convex posterior margin: dorsal cephalic shield clearly defined. Metasome with 2 incomplete dorsal sutures marking planes of fusion between first and second, and between second and third pedigerous somites. Third and fourth pedigerous somites completely fused and forming brood pouch. Freeurosome ( Fig. 284B ) 5-segmented, tapering posteriorly; genital somite much wider than long, 61×176 μm; 4 abdominalsomites 84×135, 88×116, Maxillule ( Fig. 294I ) armed as in B. brevicaudatus sp. nov., but seta on coxal endite larger. Maxilla ( Fig. 294J ) segmented and armed as in B. brevicaudatus sp. nov. Maxilliped ( Fig. 295A ) armed with 6 medial setae and 1 outer seta; apex strongly sclerotized.

Leg 1 ( Fig. 295B ) with 2-segmented rami; inner coxal seta pinnate; outer seta on basis small as in legs 2– 4. First exopodal segment lacking inner seta; compound 77×102, and 65×84 μm, respectively. Anal somite with deep posteromedian incision. Caudal ramus ( Fig. 284C ) 4.3 times longer than wide (86×20 μm): armed with 6 setae (1 proximal, 1 subdistal, and 4 distal); proximal and subdistal setae located at 30 and 76% of ramus length, respectively; 3 of 4 distal setae bluntly tipped; all setae longer than width of ramus at base.

Rostrum ( Fig. 284D ) short, muchwiderthanlong, stronglytapering distally. Antennule ( Fig. 284E ) 151 μm long, 7-segmented; armatureformula 3, 16, 4, 2+aesthetasc, 3, 1+aesthetasc, and 11+aesthetasc; setae crowded, all naked; 2 larger setae on first segment extremely long (about 1.5 times longer than entire antennule).Antenna ( Fig. 284F ) 4-segmented; short coxa unarmed; basis and first endopodal segment also unarmed, both 45×28 μm; compound distal endopodal segment about 3.1 times longer than wide (59×19 μm): armed with 9 setae arranged as 4, 2, and 3 (1 of 4 proximal setae elongate, longer than segment; longest of 3 distal setae more than twice as long as terminal claw); terminal claw small, about 0.4 times as long as segment.

Labrum ( Fig. 285G ) with large, semicircular posteromedian lobeand narrow, setulose posterior margin. Mandible ( Fig. 284H ) with 5 pointed teethand 1 small seta on coxal gnathobase: basis with 1 setaon medial margin; exopod 2-segmented with 3 setae on first segment and 2 setae on small second segment, 2 proximal setae about twice as long as distal 3: endopod 2-segmented, incompletely articulated from basis; first segment armed with 2 setae; second segment much narrower than first, with 5 setae. Paragnath ( Fig. 284I ) with prominent lobe on subdistal outer margin, and denselysetulose along medial margin. Maxillule ( Fig. 284J ) armed asin T. quadriseta sp. nov., but seta on coxal endite shorter. Maxilla ( Fig. 285A ) 5-segmented; syncoxawith 9 (3, 1, 2, and 3) setae; basis with 3 setae, distal seta slightly more than half length of middle seta; endopodwith 1, 1, and 3 setaeonfirst to third segments, respectively. Maxilliped ( Fig. 285B ) unsegmented with 8 medial and 1 outer subdistal seta.

Legs 1–4with 3-segmentedexopods and 2-segmented endopods ( Fig. 285 C-E); innercoxalsetaabsent; outer seta on basis small. Inner distal spine on basis of leg 1 not extending to distal border of first endopodal segment, 22 μm long. Second exopodal segment of leg 1 with large, tapering anterodistal process. First and second exopodal segments of legs 2–4 each with bifurcate anterodistal process. 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
Legs 2 & 30-0	30-0	1-0	1-1; 1-1; 3, 1, 5	0-1; 1, 3, 4
Leg 4	0-0	1-0	1-0; 1-0; 2, 1, 5	0-0; 1, 3, 0

Leg 5 ( Fig. 285F ) consisting of very short protopod bearing 1 seta and small, tapering free exopodal segment, 12×15 μm, armed distally with 2 setae, inner 21 μm long and outer 34 μm.

Male. Unknown.

Remarks. The two extremely long setae on the first antennulary segment and the large anterodistal process on the second exopodal segment of leg 1 serve to characterise T. longiseta sp. nov. The possession of 9 setae on the third exopodal segment of leg 3 is also an exceptional feature because this segment bears a maximum of 8 setae in all the other known species of the genus.

Figures

FIGURE 284. Thoracodelphys longiseta sp. nov., female. A, habitus, right; B, urosome, ventral; C, left caudal ramus, ventral; D, rostrum; E, antennule; F, antenna; G, labrum; H, mandible; I, paragnath; J, maxillule. Scale bars: A, 0.2 mm; B, D, 0.1 mm; C, E–G, I, J, 0.02 mm; H, 0.05 mm.

FIGURE 285. Thoracodelphys longiseta sp. nov., female. A, maxilla; B, maxilliped; C, leg 1; D, leg 2; E, leg 4; F, leg 5. Scale bars: A, B, F, 0.02 mm; C–E, 0.05 mm.

FIGURE 294. Bysone bidens sp. nov., female. A, habitus, right; B, urosome, ventral; C, left caudal ramus, ventral; D, rostrum; E, antennule; F, antenna; G, labrum; H, mandible; I, maxillule; J, maxilla. Scale bars: A, 0.2 mm; B, 0.1 mm; C, 0.05 mm; D–J, 0.02 mm.

FIGURE 295. Bysone bidens sp. nov., female. A, maxilliped; B, leg 1; C, leg 2; D, leg 4; E, leg 5. Scale bars: A, E, 0.02 mm; B–D, 0.05 mm.