The genus Oxidus Cook, 1911 is revised to contain five species, O. avia (Verhoeff, 1937), O. gigas (Attems, 1953), O. gracilis (C.L. Koch, 1847), O. riukiaria (Verhoeff, 1940), and “species inquirenda” O. obtusus (Takakuwa, 1942). A cosmopolitan species, O. gracilis, is widely found in temperate and sub-tropical regions over the world, but other species have limited distribution in restricted regions, e.g., O. gigas in northern Vietnam, O. riukiaria and O. avia in the Ryukyu Islands (Japan). Four species, O. gracilis, O. riukiaria, O. avia and O. gigas, are confirmed as different from each other in gonopod characters, coloration and body size. The status of the last species, O. obtusus, is still doubtful and requires examination of further fresh material. The phylogenetic relationships among species of Oxidus is analyzed using two fragments of the mitochondrial genes COI (Cytochrome c Oxidase subunit I) and 16S rRNA. Three species of Oxidus are clearly separated from each other; O. gigas and O. gracilis form a monophyletic sister group with O. riukiaria. The genus Oxidus is also monophyletic and more closely related to the genus Tylopus Jeekel, 1968 than to the genera Sellanucheza Enghoff, Golovatch & Nguyen, 2004 or Kronopolites Attems, 1914. In addition, an identification key to species of Oxidus is provided.

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 phylogenetic position of Bryozoa is one of the most controversial issues in metazoan phylogeny. In an attempt to address this issue, the first bryozoan mitochondrial genome from Flustrellidra hispida (Gymnolaemata, Ctenostomata) was recently sequenced and characterized. Unfortunately, it has extensive gene translocation and extremely reduced size. In addition, the phylogenies obtained from the result were conflicting, so they failed to assign a reliable phylogenetic position to Bryozoa or to clarify lophophorate phylogeny. Thus, it is necessary to characterize further mitochondrial genomes from slowly-evolving bryozoans to obtain a more credible lophophorate phylogeny.

The phylogenetic position of pycnogonids is a long-standing and controversial issue in arthropod phylogeny. This controversy has recently been rekindled by differences in the conclusions based on neuroanatomical data concerning the chelifore and the patterns of Hox expression. The mitochondrial genome of a sea spider, Nymphon gracile (Pycnogonida, Nymphonidae), was recently reported in an attempt to address this issue. However, N. gracile appears to be a long-branch taxon on the phylogenetic tree and exhibits a number of peculiar features, such as 10 tRNA translocations and even an inversion of several protein-coding genes. Sequences of other pycnogonid mitochondrial genomes are needed if the position of pycnogonids is to be elucidated on this basis.