Ostracod genus Parapolycope (Crustacea): Diversity, distribution, and phylogeny, with description of the first representative from Korea

Abstract

Parapolycope Klie, 1936 belongs to the family Polycopidae, one of the ecologically most diverse and morphologically most primitive ostracod families. Due to the small size of animals, polycopids are poorly studied and unknown in many regions of the world. We describe a new species, Parapolycope koreana sp. nov., from marine beach interstitial in Gyeongsangnam-do, South Korea. This is the first representative of the genus, and the first named polycopid species from Korea. It is very closely related to several species from marine interstitial in Japan, but differs mainly in the shape and ornamentation of the shell and morphology of the male upper lip. A cladistic analysis of the genus Parapolycope is performed to test the phylogenetic relationships between species. Although Parapolycope presently encompasses 18 species, only 15 are included in the analysis, because Parapolycope seridentata (Hartmann, 1959), Parapolycope ramunchensis (Hartmann-Schroder and Hartmann, 1962), and Parapolycope minutissima (Hartmann, 1974) differ so much from other congeners that they should be excluded from the genus. The analysis is based on 27 morphological characters, with Parapolycopissa rossica (Chavtur, 1977) and Polycopiella microdentata Chavtur, 1979 as two outgroup taxa. In spite of the fact that descriptions of almost half of species included in the analysis are based on a limited set of morphological characters, the majority rule of the 15 equally parsimonious trees undoubtedly shows that there are at least two distinct lineages in the genus, defined by the number of claws on the female uropodal lamellae. A close relationship between the new species and the Japanese congeners is also strongly supported. We redescribe the type species of the genus, Parapolycope germanica Klie, 1936, based on the type material, and designate the lectotype and paralectotypes. A key for identification of Parapolycope species is provided, along with a map of their distribution. This is a cosmopolitan taxon, with the centre of diversity in the Northwest Pacific region.