Cystixys, 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 : 523-524

Cystixys gen. nov.

Diagnosis. Body highly transformed, globular. Dorsal cephalic shield bearing paired lateral horn-like processes. Metasome unsegmented, entire metasome forming brood pouch. Free urosome 5-segmented. Caudal rami small, setose; caudalsetae indistinct. Rostrum distinct.Antennule 7-segmented. Antenna 4-segmented, with 2-segmented endopod and small terminal claw. Labrum weak. Mandible with narrow coxal gnathobase bearing 1 distal tooth and proximal pectinate region; palp armed with 1 seta on basis, 5 on exopod, and 1 and 4 on first and second endopodal segments, respectively. Maxillule armedwith 3 setaeon arthrite, 1 eachoncoxalepipoditeand basis, 4onexopodand 3 on endopod; coxal endite absent. Maxilla 4-segmented, 3 endites on syncoxa; basis with slender claw plus 1 seta; endopod small, 2-segmented with 1 and 3 setae on first and second segments, respectively; seta on first segment and 1 seta on second segment enlarged (much longer than entire maxillary segments). Maxilliped unsegmented, armed with few setae. Legs 1–4 with 3-segmented rami; inner coxal seta absent; first and second segments of both rami usually bearing inner seta. Leg 1 basis bearing inner distal spine. Leg 5 located ventrally on surface of somite and represented by outer protopodal seta and inner (exopodal) process bearing outer margin seta. Living in gall formed on branchial tissue of ascidian host.

Type and only species. Cystixys globosa gen. et sp. nov. by original designation.

Etymology. The generic name comes from the Greek cyst (= bladder) and ixys, the ending of several generic names in the family Notodelphyidae : it refers to the mode of life of the type species, living inside a cyst within a gall. Gender feminine.

Remarks. There are two significant autapomorphic features characterising the new genus. Firstly, the shape of the mandibular coxal gnathobase is characteristic with the cutting edge consisting of a single distal tooth and a pectinate proximal region. The second feature is the presence of 2 extremely large setae on the endopod of the maxilla: these setae are longer than the limb itself.

The armature of the mouthparts is markedly reduced in Cystixys gen. nov. In particular, there are only 3 setae on the arthrite of the maxillule and only 2 setae on the maxilliped. In contrast, the armature of swimming legs is relatively well conserved, retaining the inner seta on the first and second segments of all swimming legs.