Sympygus, 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 : 410-413

Sympygus gen. nov.

Diagnosis. Body of female laterally compressed, Doropygus -shaped, covered with thick exoskeleton. Prosome clearly 5-segmented, comprising cephalosome and 4 pedigerous somites; fourth pedigerous somite forming brood pouch, largely incorporating fifth pedigeroussomite. Freeurosome 5-segmented. Caudal ramus armed with 6 setae. Rostrum short, fused at base. Antennule slender, 9-segmented. Antenna consistingof coxa, basis, and 2-segmented endopod withterminal claw; exopod absent. Mandible with narrow coxal gnathobase bearing 2 teeth; basiswith 1 seta; exopodwith 4 setae; endopod 2-segmented with 4 and 10 setae on first and second segments, respectively. Maxillulewith 8 setae on arthrite; coxa with 2 setae on epipodite, but endite absent; exopod and endopod fused with basis forming complex lacking any subdivision, armed with total of 7 setae. Maxilla 5-segmented; syncoxawith 3, 2, and 2 setae on first to third endites, respectively; basis with 2 setae; endopod 3-segmentedwith 1, 1, and 3 setaeonfirst to third segments, respectively. Maxilliped unsegmented with 5 medial and 2 apical setae. Legs 1–4 segmented and armed as in Doropygus . Leg 4 lacking inner coxal seta and inner setaon first exopodal segment. Leg 5 small, but 2-segmented; armed with 1 setaon protopod and 2 setae on free exopodal segment.

Type species. Sympygus punctatus gen. et sp. nov., by original designation.

Etymology. The generic name is derived from the Greek sym (=together) and pygus, the ending of many generic names in the family Notodelphyidae . It alludes to the fusion of the basis, exopod and endopod of the maxillule. Gender masculine.

Remarks. The characteristic features of Sympygus gen. nov. are displayed by the maxillule which lacks a coxal endite, and in which the basis, exopod and endopod are all fused to form a single complex. Although this form of maxillule resembles that of Sesir in part, it cannot be placed in Sesir due to the other major differences in body form. In addition, in Sesir both the coxal endite and the epipodite are lacking from the maxillule, whereas the new genus retains a normal epipodite with 2 setae, and the armature of legs 1–5 is reduced in Sesir , but not in Sympygus gen. nov.

In the Notodelphyidae the fusion of the exopod, the endopod, or both rami with the basis of the maxillule has been reported in several other genera, including Demoixys Illg & Dudley, 1961 , Mesoixys Illg & Dudley, 1965 , and Paralobodelphys Gotto, 1981 . However, Sympygus gen. nov. is not related to these genera because they have an inflated or globular body form, the segmentation and setation of swimming legs are significantly reduced, and leg 5 is vestigial or absent.