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.

The first complete mitochondrial genome (17,159 bp) of the Hodgson's bat Myotis formosus, which is an endangered species in South Korea, was sequenced and characterized. The genome included 13 protein-coding, 22 tRNA, and 2 rRNA genes, and 1 control region. It has high AT content and the same gene arrangement pattern as those of typical vertebrate mitochondrial genome. Within the control region, a 80 bp tandem repeat unit was iterated five times which was found in Domain I. It has been observed only in the vespertilionid bat group, and could contribute to identifying the species or genus, and also distinguishing it from other bat families.

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Freshwater mussels belonging to the genus Nodularia (Family Unionidae) are known to be widely distributed in East Asia. Although phylogenetic and population genetic studies have been performed for these species, there still remain unresolved questions in their taxonomic status and biogeographic distribution pathways. Here, the nucleotide sequences of CO1 and 16S rRNA were newly determined from 86 N. douglasiae and 83 N. breviconcha individuals collected on the Korean Peninsula. Based on these data, we revealed the following results: (1) N. douglasiae can be divided into the three genetic clades of A (only found in Korean Peninsula), B (widely distributed in East Asia), and C (only found in the west of China and Russia), (2) the clade A is not an independent species but a concrete member of N. douglasiae given the lack of genetic differences between the clades A and B, and (3) N. breviconcha is not a subspecies of N. douglasiae but an independent species apart from N. douglasiae. In addition, we suggested the plausible scenarios of biogeographic distribution events and demographic history of Nodularia species.

Horseshoe crabs (order Xiphosura) are often referred to as an ancient order of marine chelicerates and have been considered as keystone taxa for the understanding of chelicerate evolution. However, the mitochondrial genome of this order is only available from a single species, Limulus polyphemus. In the present study, we analyzed the complete mitochondrial genomes from two Asian horseshoe crabs, Carcinoscorpius rotundicauda and Tachypleus tridentatus to offer novel data for the evolutionary relationship within Xiphosura and their position in the chelicerate phylogeny. The mitochondrial genomes of C. rotundicauda (15,033 bp) and T. tridentatus (15,006 bp) encode 13 protein-coding genes, two ribosomal RNA (rRNA) genes, and 22 transfer RNA (tRNA) genes. Overall sequences and genome structure of two Asian species were highly similar to that of Limulus polyphemus, though clear differences among three were found in the stem-loop structure of the putative control region. In the phylogenetic analysis with complete mitochondrial genomes of 43 chelicerate species, C. rotundicauda and T. tridentatus were recovered as a monophyly, while L. polyphemus solely formed an independent clade. Xiphosuran species were placed at the basal root of the tree, and major other chelicerate taxa were clustered in a single monophyly, clearly confirming that horseshoe crabs composed an ancestral taxon among chelicerates. By contrast, the phylogenetic tree without the information of Asian horseshoe crabs did not support monophyletic clustering of other chelicerates. In conclusion, our analyses may provide more robust and reliable perspective on the study of evolutionary history for chelicerates than earlier analyses with a single Atlantic species.