Bysone Stock & Humes, 1970

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 : 441

Genus Bysone Stock & Humes, 1970

Diagnosis. Body of female curved ventrally. Prosome expanded posteriorly; third and fourth pedigerous somites or fourth pedigerous somite alone forming brood pouch. Freeurosome 5-segmented. Caudal rami armedwith 6 setae. Rostrum present. Antennule 6-segmented. Antenna 4-segmented with terminal claw. Mandible consistingof coxal gnathobase with broad cutting margin, and palp comprising basis, 1-segmented exopod bearing 4 setae, and 2-segmented endopod bearing 2 and 5 setaeonfirst and second segments, respectively. Maxillule armed with 7 to 9 setaeon arthrite, 1 on endite, 2 on epipodite, 3 on basis, 3 onexopodand 2 on endopod. Maxilla 4- or 5- segmentedwith 2- or 3-segmented endopod. Maxilliped unsegmented, armed with 5 to 8 setae medially and 1 seta subdistally on outer margin. Leg 1 with 2-segmented rami; inner coxal seta present; basis without inner distal spine; first exopodal segment lacking inner seta. Legs 2–4 with 3-segmented exopods and 2-segmented endopods. Inner coxal seta present or absent on legs 2–4. Leg 5 reduced; exopod lobate or digitiform, armed with 2 setae distally.

Type species. Bysone operculatus Stock & Humes, 1970 , by original designation.

Remarks. Like Thoracodelphys , Bysone carries 2 and 5 setae, respectively, on the first and secondendopodal segments of the mandible, and 3 and 2 setae, respectively, on the exopod and endopod of the maxillule. It also has a reduced leg 5, a reduced number of antennular segments, and a maxilliped that is similar to that of Thoracodelphys . Unlike Thoracodelphys , the body of Bysone is not dorsoventrally depressed, the exopod of leg 1 is only 2- segmented, and the inner coxal seta is present at least on leg 1. In addition, the setation of the swimming legs is better developed so that the distal endopodal segments of legs 1 and 4 are armed with 7 setae (in Thoracodelphys the same segment is armed invariably with only 6 setae in leg 1 and with only 4 setae in leg 4). Finally, the bifurcate distal process on surface of the second exopodal segment of legs 2–4, which is typical of species of Thoracodelphys , is absent in Bysone .