Thoracodelphys Stock, 1967

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 : 421-424

Genus Thoracodelphys Stock, 1967

Diagnosis. Body of female small. Prosome dorsoventrally depressed and tapering anteriorly. Free urosome 5- segmented. Caudal rami slender, armed with 6 setae or mix of spines plus setae. Rostrum small and short. Antennule small, stout, 6- or 7-segmented; setae generally long. Antenna 4-segmented, including 2-segmented endopod tipped with claw; exopod absent. Mandible with 5 teeth on coxal gnathobase; basis with 1 medial margin seta; exopodwith 4 or 5 setae; endopodwith 2 and 5 setaeon firstandsecondsegments, respectively. Maxillulewith 7 or 8 setae on arthrite, 1 on coxal endite, 2 on epipodite, 3 on basis, 3 onexopodand 2 on endopod. Maxilla 5-segmented; basis armed only with setae; endopod 3- segmented. Maxilliped unsegmented with 6 to 8 setae medially and 1 outer seta subdistally. Legs 1–4 biramous with 3-segmented exopods and 2-segmented endopods; inner coxal seta absent. Leg 1 with inner distal spine on basis. Second exopodal segment of legs 2–4 with large, bifurcate anterodistal process. Inner seta usually absent on first and second exopodal segments of posterior swimming legs. Armature formula for endopods of legs 1–4: 0-0; 1, 2, 3 (leg 1), 0-1; 1, 2, 5 (legs 2 and 3), and 0-0; 1, 2, 1 (leg 4). Leg 5 reduced, consisting at most of short protopod bearing outer seta and small, lobate exopodal segment bearing 2 setae.

Type species. Thoracodelphys chelipus Stock, 1967 , by original designation.

Remarks. When establishing Thoracodelphys, Stock (1967) recognized it as a close relative of Bonnierilla and separated it from the latter genus by its reduced leg 5, the 2-segmented endopod of leg 1, the reductions in the armature of the maxilliped and maxillulary exopod and endopod, and by the reduction in the segmentation and setation of the antennule. Stock & Humes (1970) added a second species, T. uniseta Stock & Humes, 1970 , and here we describe six new species. The discovery of all these additional species in the genus has revealed some other shared generic characters, such as the depressed body with its anteriorly tapering prosome, the presence of the bifurcate anterodistal process on the second exopodal segment of legs 2–4, the armature of the mandibular endopod, and the setation pattern of the endopods of legs 1–4. Species within the genus appear to exhibit a trend in caudal setation, with the more distal setae on the caudal rami being transformed into spines.

Females of the known species of Thoracodelphys can be identified using the following key:

1. Caudal ramus more than 9 times longer than wide; mandibular exopod armed with 4 setae; third endopodal segment of maxilla with 2 setae ...... T. quadriseta sp. nov.

Caudal ramus lessthan 7 times longer than wide; mandibular exopod armed with 5 setae; third endopodal segment of maxilla with 3 setae .......................................................... 2

2. Maxilliped armedwith 7 (6+1) setae................................ 3

Maxilliped armedwith 8 (7+1) or 9 (8+1) setae .............. 4

3. First exopodal segment of legs 2–4 with simple anterodistal process; legs 2 and 3 lacking inner seta.............................. ....................................................... T. chelipus Stock, 1967

First exopodal segment of legs 2–4 with bifurcate anterodistal process; legs 2 and 3 with inner seta...................................................... T. uniseta Stock & Humes, 1970

4. First exopodal segments of legs 2–4 each with outer spine ................................................................ T. tertius sp. nov.

First exopodal segments of legs 2–4 each with outer seta or lacking outer element ....................................................... 5

5. Maxilliped with 8 (7+1) setae; third exopodal segment of leg 2 armed with total of 8 setae; first exopodal segment of leg 2 lacking outer element ............... T. papuensis sp. nov.

Maxilliped with 9 (8+1) setae; third exopodal segment of leg 2 armed with total of 9 setae; first exopodal segment of leg 2 bearing outer seta..................................................... 6

6. Third exopodal segment of leg 3 armed with total of 9 setae; second exopodal segment of leg 1 bearing large outer distal process .............................................. T. longiseta sp. nov.

Third exopodal segment of leg 3 armed with 8 setae; second exopodal segment of leg 1 lacking outer distal process ... 7

7. First and second exopodal segments of leg 3 each with inner seta; first and second exopodal segments of leg 4 unarmed ............................................................ T. depressa sp. nov.

First and second exopodal segments of leg 3 without inner seta; first and second exopodal segments of leg 4 each with outer seta......................................... T. caledonica sp. nov.