Genus Hemicytherura (Crustacea, Ostracoda) in Korea with description of a new species and the first insight into its molecular phylogeny

Abstract

Hemicytherura Elofson, 1941 contains over 100 species globally, described mostly from fossil and subfossil assemblages. They are minute, mostly phytal ostracods, with an intricate pattern of fossae and muri on the surface of the shell. This pattern has been used to define four species groups in the genus, but only 10 living species from Japan and Taiwan have been classified using this labelling. Eight species have been reported so far from Korea, albeit mostly briefly. Here we study six species, collected from eight littoral localities on the South Korean mainland and Jeju Island: Hemicytherura cuneata Hanai, 1957; Hemicytherura japonica Kaseda & ikeya, 2011; Hemicytherura kajiyamai Hanai, 1957; Hemicytherura occidens n. sp., Hemicytherura okuboi Kaseda & ikeya, 2011; and H. sp. The new species is proposed based on morphological and genetic differences in partial ITS and CO1 regions; these two genes were also used to test the phylogenetic basis of the existing species groups. Morphologically, H. occidens is very similar to Hemicytherura huangi Kaseda & ikeya, 2011, Hemicytherura notoensis Kaseda & ikeya, 2011, and H. okuboi, but differs from all three in the appearance of the outer clasping apparatus on the hemipenis. Phylogenetic tree resulting from the analysis of the ITS region (but not CO1) supports a close relationship of the new species with H. kajiyamai and H. okuboi (both members of the kajiyamai-group) with high posterior probabilities. The other three Korean species studied belong to the cuneata-group. The existing four groups are used to classify another 25 Hemicytherura species, and two new groups (anomala and clathrata) are proposed for further 18 species. Our new groups are also based on the surface ornamentation of the shell, but without using fossae and muri labelling.