Janius, 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 : 588-590

Janius gen. nov.

Diagnosis. Body maggot-like, cylindrical. Prosome consisting of clearly defined cephalosome and unsegmented metasome with very reduced, unsegmented, free urosome inserted into ventral surface of prosome. Caudal rami broadly elliptical, ornamented with setules; setal armature uncertain. Antennule lobate, tapering; surface densely covered with setules. Antenna consisting of coxa, basis, and unsegmented endopod bearing small terminal claw. Mandible with broad coxal gnathobase bearing pectinate medial margin; palp with elongate basis bearing 1 seta; exopod rudimentary, represented by small, unarmed swelling; endopod obscurely defined from basis, 2-segmented, armed with 1 and 4 setae on first and second segments, respectively. Maxillule unsegmented, armed with 4 mediodistal and 5 outer subdistal setae. Maxilla 3-segmented; armedwith 2 setaeonsyncoxa, 1 setaon basis, and 2 setaeon unsegmented endopod. Maxilliped unsegmented with 4 setae. Leg 1 biramous, positioned just posterior to oral area, directed anteriorly; exopod 1-segmented; endopod obscurely 2-segmented. Leg 2 rudimentary, represented by 2 setae. Legs 3-5 absent.

Type species. Janius brevis ( Stock, 1967) comb. nov. (originally as Prophioseides brevis Stock ) by original designation.

Etymology. The generic name honours the late Prof. Jan H. Stock who discovered the type species of the new genus. Gender masculine.

Remarks. The mandible of Prophioseides brevis Stock, 1967 is very unusual for the genus Prophioseides , because the exopod is reduced to a semicircular, unarmed swelling. Stock (1967) described this species on the basis of a single specimen and did not determine whether the reduction of the mandibular exopod was a normal condition or a deformity resulting from injury or damage. However, Stock (1967) mentioned that the left and right mandibles are of the same form, from which we infer that this is the normal structure of mandible for this species. Stock (1967) mentioned other differences between P. brevis from its congeners: the body is shorter and thicker, the abdomen is inserted ventrally, the caudal rami are broadly elliptical, and the species is associated with the solitary ascidian Phallusia nigra Savigny, 1816 in the Red Sea, in contrast to the association of all other congeneric species with the compound ascidians.

Prophioseides brevis cannot be accommodated in Prophioseides without an unacceptable broadening of the generic diagnosis, and therefore a new genus, Janius gen. nov., is established here to accommodate this species, as Janius brevis ( Stock, 1967) comb. nov.