New benthopelagic bradfordian calanoids (Crustacea: Copepoda) from the Pacific Ocean with comments on generic relationships

Abstract

Three new bradfordian genera, and Rythabis heptneri sp.n. and R. schulzi sp.n. are described. Brodskius gen.n. has a narrow mandibular gnathobase with 2 distinct incisions separating groups of teeth, maxilla 1 with 1 long, thick and heavily setulated seta on proximal basal endite and 2 such setae on distal basal endite plus endopod, and setae on the distal basal endite of maxilla 1 inseparable from those of endopod. The new genus includes species formerly known as Amallothrix robustipes Grice, Hulsemann, 1965 and Xanthocalanus paululus Park, 1970, and B. benthopelagicus sp.n. and B. confusus sp.n., the latter proposed for the paratypes of Xanthocalanus paraincertus Grice, Hulsemann, 1965 which are not conspecific with the holotype. An unnamed male of Brodskius is also described. Xanthocalanus hispidus Grice, Hulsemann, 1967 is not a synonym of B. paululus. Byrathis gen.n., has the proximal 2 terminal setae on praecoxal endite of maxilla 1 curved proximally, and includes Xanthocalanus macrocephalon Grice, Hulsemann, 1970, B. volcani sp.n., and B. laurenae sp.n.; a poorly-preserved, unnamed female of Byrathis also is described. Omorius gen.n. with the 3 rd and 4 th setae on the praecoxal endite of maxilla 1 thin and slightly curved is established for Omorius atypicus sp.n. Indistinctly separated groups of setae of the praecoxal endites of the maxilliped is a synapomorphy of Rythabis. Evolutionary relationships of the new genera to several known bradfordian genera are inferred from an initial loss of one or two setae on the distal praecoxal endite of the maxilliped followed by transformations of sclerotized setae on all praecoxal endites of the maxilliped, and the loss of setae and arthrodial membranes to the exopod of antenna 2. Different pelagic or benthopelagic ancestors to the genera comprising both Phaennidae and Scolecitrichidae suggest these pelagic families are not their own closest relatives. Adaptation to detritivory appears to have resulted in the significant morphological variability of bradfordian calanoid copepods.