Pertsovius Andronov & Kosobokova, 2011, gen. nov.

Genus Pertsovius gen. nov.

Diagnosis. Small calanoid copepods with body length seldom exceeding 1 mm. Prosome of females of oval shape, anterior head rounded. Cephalon fully or partly separated from first pediger, fourth and fifth pedigers completely fused. Urosome consisting of four free somites. Genital double somite usually expanded laterally and protruding ventrally, frequently forming very large fold. Caudal rami usually of unequal lengths, longer on left; each bearing four setae, with outer setae shorter and thinner than others; outer seta on left ramus usually longer and thicker than corresponding seta on right one. Rostrum large, obtusely rounded, directed ventrally, without filaments. Antennule consisting of 24–25 free segments, with ancestral segments I–III fused, segments IX–XI separate, distal ancestral segments XXVI and XXVII + XXVIII often fused, but in Disco fiordicus Fosshagen, 1967 and D. oceanicus Gordejeva, 1974 segments XXVI and XXVII + XXVIII separate. Antenna, mandible, maxillule and maxilliped of same structure in all species of genus. Antenna exopod longer than endopod. Mouthparts relatively well developed compared to other discoid genera. Mandible endopod and exopod similar in length; cutting edge of gnathobase bearing five to seven large unicuspidate teeth. Maxillule bearing six setae on first inner lobe, two setae on second inner lobe, one seta on basis, eight setae on endopod, two setae on exopod, and four setae on outer lobe. Maxilla first lobe with four setae, second to fourth lobes two setae each, fifth lobe with one seta, and endopod with four setae. Maxilliped with well-developed syncoxa and basis, bearing five-six setae on syncoxa and two setae on basis; endopod with five free segments with setal formula 1.2.2.2.3. P1-P4 coxae and basis have no setae, endopods typically one-segmented and exopods three-segmented, with exception of D. longus Grice & Hulsemann, 1965, where Р4 endopod two-segmented. Endopods of Р1-P4 bearing three, four, five and five setae, respectively. Distal segment of Р1 exopod with two lateral spines, of Р2 with two or three, and of Р3 and Р4 with three outer border spines. Surface of P1-P4 rami not ornamented. P5 absent. Male unknown.

Type species. Pertsovius tridentatus gen. et sp. nov.

Other species. Р ertsovius longus (Grice & Hulsemann, 1965); Р. fiordicus (Fosshagen, 1967) (only female); Р. oviformis (Park, 1970); Р. oceanicus (Gordejeva, 1974); P. heterodentatus gen. et sp. nov. and P. serratus gen. et sp. nov.

Etymology. The generic name is proposed in the memory of Nikolay Andreevich Pertsov (1924–1987), the founder and a well-known Head of the White Sea Biological Station (“Nikolay Pertsov White Sea Biological Station”, WSBS) of the Moscow State University (MSU) from 1951 to 1987. Employees of WSBS, professors of the Biological Department of the MSU and former students, ourselves included, first became acquainted with marine biota at the WSBS, and remember this remarkable person with great affection. Gender masculine.

Differential diagnosis. The species of the new genus Pertsovius gen. nov. have one-segmented endopods of Р2-Р4 (with exception of Disco longus). In contrast, the representatives of the other genera of this family have three-segmented endopods of Р2-Р4. Maxillule, maxilla and maxilliped with complete armature.

Remarks. The family Discoidae Gordejeva, 1975 currently includes 29 species (Razouls et al. 2005–2010) belonging to three genera: Disco Grice & Hulsemann, 1965; Prodisco Gordejeva, 1975 and Paradisco Gordejeva, 1975. Only females are currently described in the majority of these species. Some males are also described, but their assignment to particular species is debatable. For example, the female and male Disco fiordicus Fosshagen, 1967 are very similar in appearance of prosome; however, the specific details of their Р1-Р 4 may indicate their affinity to different genera.

Research on the Discoidae in the high Arctic is just beginning. Only one species within this family, Disco triangularis Markhaseva & Kosobokova, 1998 has been reported so far poleward of 80°N. The most northerly record of the other known species is about 60°N (D. fiordicus Fosshagen, 1967). All other Discoidae were found further south (Grice & Hulsemann 1965, 1967; Fosshagen 1967; Gordejeva 1974a, 1974b, 1974c, 1975a, 1975b, 1976; Schulz 1993, 2003). It is noteworthy that the species of this family are inhabitants of bathy- and mesopelagic depths, where conditions are fairly constant across different climatic zones. Hence, one might expect to find the species described from lower latitudes also in high latitudes. Thus, processing samples from the Arctic Ocean we often encountered D. hartmanni Schulz, 1993, originally described from samples collected at 41°36’ N, 09°30’ W (Kosobokova et al. in press).

Several species within the family Discoidae are very similar to each other: Disco longus Grice & Hulsemann, 1965; D. fiordicus Fosshagen, 1967 (only female); D. oviformis Park, 1970 and D. oceanicus Gordejeva, 1974a.

Park (1970) and Schulz (1993) noted their close similarity, which could warrant their placement within a unique taxonomic clade. The discovery of three additional species affiliated with this clade during the present study in the Arctic Ocean further warrants erection of a distinct genus. Here, the new genus, Pertsovius, is created for this group of seven species, along with the description of three new species within this genus.