A large collection of kinorhynch specimens from coastal and subtidal localities around the Korean Peninsula and in the East China Sea was examined, and the material included several species of undescribed or poorly known species of Echinoderes Claparède, 1863. The present paper is part of a series dealing with echinoderid species from this material, and inludes descriptions of four new species of Echinoderes, E. aspinosus sp. nov., E. cernunnos sp. nov., E. microaperturus sp. nov. and E. obtuspinosus sp. nov., and redescriprion of the poorly known Echinoderes tchefouensis Lou, 1934.

Copepods, small aquatic crustaceans, are the most abundant metazoan zooplankton and outnumber every other group of multicellular animals on earth. In spite of ecological and biological importance in aquatic environment, their morphological plasticity, originated from their various lifestyles and their incomparable capacity to adapt to a variety of environments, has made the identification of species challenging, even for expert taxonomists. Molecular approaches to species identification have allowed rapid detection, discrimination, and identification of cryptic or sibling species based on DNA sequence data. We examined sequence variation of a partial mitochondrial cytochrome C oxidase I gene (COI) from 133 copepod individuals collected from the Korean Peninsula, in order to identify and discriminate 94 copepod species covering six copepod orders of Calanoida, Cyclopoida, Harpacticoida, Monstrilloida, Poecilostomatoida and Siphonostomatoida. The results showed that there exists a clear gap with ca. 20 fold difference between the averages of within-specific sequence divergence (2.42%) and that of between-specific sequence divergence (42.79%) in COI, suggesting the plausible utility of this gene in delimitating copepod species. The results showed, with the COI barcoding data among 94 copepod species, that a copepod species could be distinguished from the others very clearly, only with four exceptions as followings: Mesocyclops dissimilis–Mesocyclops pehpeiensis (0.26% K2P distance in percent) and Oithona davisae–Oithona similis (1.1%) in Cyclopoida, Ostrincola japonica–Pseudomyicola spinosus (1.5%) in Poecilostomatoida, and Hatschekia japonica–Caligus quadratus (5.2%) in Siphonostomatoida. Thus, it strongly indicated that COI may be a useful tool in identifying various copepod species and make an initial progress toward the construction of a comprehensive DNA barcode database for copepods inhabiting the Korean Peninsula.

Preliminary surveys of brackish and freshwater habitats in the southeast and east of South Korea produced a total of fifteenspecies. Ten of these species are new records for Korea, and one additional species, belonging to the genus Tanycypris, isnewly described herein. Twenty-seven species of nonmarine ostracods are now reported from Korea, but this is probablyonly a small proportion of the actual number of species inhabiting the peninsula. The presence of Dolerocypris ikeyaiSmith & Kamiya, 2006, Cryptocandona brehmi (Klie, 1934), Cryptocandona tsukagoshii Smith, 2011, Physocypria nip-ponica Okubo, 1990 and Vestalenula cylindrica (Straub, 1952) on the Korean Peninsula demonstrates that these species are also distributed on the continent, and are not endemic to Japan.

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Meristoderes is the most recently described kinorhynch genus and has until now only accommodated its type species M. macracanthus from the Mediterranean and M. galatheae from the Solomon Islands in Southeast Asia. The present contribution is an account on the genus based on samples from the ongoing exploration of the kinorhynch fauna in coastal and subtidal waters around in the Korean Peninsula. The samples yielded no less than five new species of Meristoderes, of which four are formally described herein, whereas only diagnostic notes are provided for the fifth. The descriptions are supplemented with a key to species of the genus, and morphological notes on the organization of cephalic structures and cuticular trunk structures. New morphological findings include intrageneric variation in the composition of the terminal segment, which may have either one unpaired or two paired tergal plates. The data also show that the differentiation of a tergal and sternal plate in segment 2 varies greatly between the species. Results of the present study indicate that the genus probably holds a significant, unrecovered biodiversity, but the data also shed light on potential future taxonomic problems among genera of Echinoderidae and stress the importance of identifying additional diagnostic traits to define Meristoderes.