Thoracodelphys quadriseta, 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

Thoracodelphys quadriseta sp. nov.

( Figs. 282 , 283 )

Type material. Holotype ♀ (dissected and mounted on a slide, MNHN-IU-2014-21348 ) from Botrylloides anceps (Herdman, 1891) , Canal Woodin , Grand Terre, New Caledonia, depth 20 m, Monniot coll., 17 September 1985.

Etymology. The specific name refers to the possession by the new species of four setae on the mandibular exopod.

Descriptionoffemale. Body ( Fig. 282A ) relatively narrow, slightly depressed; bodylength 1.00 mm. Prosome 727 μm long, with almost truncate posterior margin: cephalosome relatively large, well defined from metasome. Metasome broadening posteriorly, with first to fourth pedigerous somites defined by incomplete dorsal sutures. Freeurosome ( Fig. 282B ) slender: genitalsomite short but much wider than abdomen, strongly tapering posteriorly, 39×147 μm. Four abdominal somites 70×89, 59×83, 56×76, and 53×71 μm, respectively: anal somite narrowing posteriorly, with deep posteromedian incision. Caudalramus ( Fig. 282C ) very slender, about 9.9 times longer than wide (128×13 μm) and about 2.4 times longer than anal somite: probably armed with 5 setae; outer proximal and dorsal setae located at 27 and 71% of ramus length, respectively.

Rostrum short withrounded apex. Antennule ( Fig. 282D ) 124 μm long, 7-segmented; third and fourth segments subdivided on posterior surface; armature formula 2, 16+spine, 7+aesthetasc, 3, 2+aesthetasc, 3+aesthetasc, and 7+aesthetasc; setae crowded, all naked; setae on first segment larger than other setae, but shorter than entire antennule; spine on secondsegment ornamented with spinules along anterior margin. Antenna ( Fig. 282E ) 4-segmented; coxa unarmed; basis and first endopodal segment also unarmed, each 37×25 and 44×26 μm; compound distal endopodal segment about 3.2 times longerthanwide (57×18 μm): armedwith 5 setae (2 subdistal and 3 distal) plus terminal claw, 31 μm long.

Labrum ( Fig. 282F ) with semicircular posteromedial lobe and feebly setulose, convex posterior margin. Mandible ( Fig. 282G ) with 5 pointed teeth and 1 small seta on coxal gnathobase: basis with 1 seta on medial margin; exopodwith 4 large setae; endopod 2-segmented; first segment with 2 setae; second segment distinctly narrower than first, armedwith 5 setae. Maxillule ( Fig. 282H ) with 8 setae on arthrite, 1 seta on coxal endite, 2 unequal setae on epipodite, 3 setae (1 small proximal and 2 larger distal) on basis, 3 setae on exopod and 2 setae on endopod. Maxilla ( Fig. 282I ) 5-segmented; syncoxawith 9 setae (3, 1, 2, and 3 on first to fourth endites, respectively); basis with 3 setae, distal seta less than half length of middle seta; endopod 3-segmentedwith 1, 1, and 2 setaeonfirst to third segments, respectively. Maxilliped ( Fig. 283A ) unsegmented with 8 medial setae and 1 outer seta.

Legs 1–4with3-segmented exopodsand 2-segmented endopods ( Fig. 283 B-E); innercoxalsetaabsent. Inner distal spine on basis of leg 1 small, naked, 19 μm long, extending to distal border of first endopodal segment: anterodistal process on first exopodal segment small in legs 1 and 4, but larger in legs 2 and 3. Anterodistal process on second exopodal segment small and simple in leg 1, but large and bifurcate in legs 2–4. First exopodal segment of legs 1–4 bearing large outer distal spine; this spine bluntly tipped extending beyond distal border of second exopodal segment. Outer setae on second and third exopodal segments and distal setae on third exopodal segments of legs 2–4 bluntly tipped. Armature formula for legs 1–4 as in T. tertius sp. nov. Leg 5 ( Fig. 283F ) similar to that of T. tertius sp. nov., but exopodal segment articulated at base.

Male. Unknown

Remarks. This new species is comparable with T. tertius sp. nov. in having an outer spine, rather than an outer seta, on the first exopodal segment of legs 2–4. But it can be distinguished from T. tertius sp. nov. and other congeners by two unique features: firstly, the mandibular exopod is armed with 4 setae (instead of 5 setae as in all congeners), and secondly, the maxillary endopod is armed with 1, 1, and 2 setae on the first to third segments, respectively (instead of 1, 1, and 3 as in all congeners). Theextremely slendercaudal ramus alsois a characteristic feature of T. quadriseta sp. nov., since it is more than 9 times longer than wide compared to less than 7 times longerthan wide in all known congeners.

Figures

FIGURE 282. Thoracodelphys quadriseta sp. nov., female. A, habitus, right; B, urosome, ventral; C, left caudal ramus, ventral; D, antennule; E, antenna; F, labrum; G, mandible; H, maxillule; I, maxilla. Scale bars: A, B, 0.1 mm; C–I, 0.02 mm.

FIGURE 283. Thoracodelphys quadriseta sp. nov., female. A, maxilliped; B, leg 1; C, leg 2; D, exopod of leg 3; E, leg 4; F, leg 5. Scale bars: 0.02 mm.