Pentachaetus, 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 : 494

Pentachaetus gen. nov.

Diagnosis. Body form as in Doroixys . Dorsal cephalic shield bearing paired horn-like processes posterolaterally. Fifth pedigerous somite fused with fourth. Free urosome 5-segmented. Caudal ramus bearing 5 well-developed setae (2 proximal and 3 distal). Rostrum well-developed. Antennule 6-segmented; first segment armed with 2 setae. Antenna 3-segmented, comprising coxa, basis, and unsegmented endopod; terminal claw small. Labrum weak, flexible. Mandible similar to that of Doroixys ; exopod armed with 5 setae; endopod 2-segmented with 1 seta on first segment and 4 setae on second. Maxillule as in Doroixys , lacking coxal endite. Maxilla 4-segmented, bearing 4 setae on first endite of syncoxa, claw plus 2 setaeon basis, and 2-segmented endopodarmedwith 1 and 3 setae on first and second segments, respectively. Maxilliped unsegmented with 6 setae. Leg 1 with 2- or 3-segmented exopod and 3-segmented endopod; second exopodal segment (or original second exopodal segment) lacking outer element. Leg 2 with 3-segmented rami. Legs 3 and 4 with 3-segmented exopods and 2-segmented endopods. Inner coxal seta absent in legs 1–4. First and second exopodal segments of legs 2–4 lacking inner seta. Legs 2–4 with setal armature only on terminal endopodal segments. Leg 5 represented by 2 processes and 2 setae.

Etymology. The generic name is derived from the Greek penta (=five) and chaet (=a bristle) and refers to the presence of five setae on the caudal ramus. Gender masculine.

Typespecies. Pentachaetusspinatus gen. etsp. nov. by original designation.

Other included species. Pentachaetus palauensis gen. etsp. nov. and P. longisetatus gen. etsp. nov.

Remarks. The three species placed in this new genus constituteahomogeneousgroup andcanbe separatedfrom the closely related genus, Doroixys , by two prominent features: firstly, the caudal ramus is armedwith 5 (not 6) well-developed setae, and secondly, the second exopodal segment (or original second exopodal segment) of leg 1 lacks an outer setal element.