Of the four species in the genus Cadlina present in the northwestern Pacific region, C. japonica has been the only species recorded from South Korea. For the purpose of investigating Cadlina in Korean waters, specimens were collected from the Korean East Sea (Sea of Japan) by scuba diving. The radula and morphology of these specimens were examined by stereoscopic and scanning electron microscopy. Based on morphology, three species were identified in Korean waters, including the new species, Cadlina koreanasp. nov., C. umiushi (first record in South Korea), and C. japonica. Cadlina koreanasp. nov. somewhat resembles C. umiushi but differs in both its morphology as well as the structure of its radula. The background color of Cadlina koreanasp. nov. is translucent white, tubercles on the dorsum are opaque white and the yellow marginal band is absent. The radular formula of Cadlina koreanasp. nov. is 57 × 23.1.23 with a rectangular rachidian tooth. In addition, mitochondrial cytochrome c subunit 1 (COI), 16S ribosomal RNA (16S rRNA), and nuclear 28S ribosomal RNA (28S rRNA) gene sequences were generated and used for analysis of Automatic Barcode Gap Discovery (ABGD) and reconstruction of the phylogenetic tree. Morphological distinction and genetic analyses confirm that three Cadlina species are present in Korean waters of which Cadlina koreana is a new species.
The Littorinid snail Littorina (Littorina) kasaka Reid, Zaslavskaya & Sergievsky, 1991, from Kandwon-do, Korea was recorded as new to the Korean molluscan fauna. Including the new recorded in this study, the family Littorinidae contained seven genera and 16 species in the Korean water.
The complete mitochondrial genome sequence of the crested auklet, Aethia cristatella, was obtained using high-throughput whole genome sequencing. This is the first report indicating that the complete mitochondrial genome of Aethia has been sequenced. The circular genome is 16,848 bp in length. It contains thirteen protein-coding genes, twenty-two transfer RNAs, two ribosomal RNAs, and a control region. The ND3 gene possessed an insertion mutation. Maximum likelihood phylogenetic analysis demonstrated that A. cristatella is the sister clade of P. aleuticus clustered with the Alcinae species, belonging to Alcidae.
The North Pacific nudibranch species Triopha catalinae (Cooper, 1863), also known as the clown nudibranch, includes two distinct morphotypes: the trans-Pacific morphotype, known from South Korea to Southern California, and the eastern Pacificonly morphotype from Southeast Alaska to Baja California. We tested the hypothesis that Triopha catalinae is a species complex by applying an integrative taxonomic approach that included (1) phylogenetic analyses of the mitochondrial 16S and COI, and the nuclear Histone H3 genes; (2) haplotype network analysis based on COI sequences; (3) Automatic Barcode Gap Discovery (ABGD) species delimitation analysis based on 16S and COI sequences; and (4) comparative internal and external morphological studies. Specimens of two morphotypes were found to be genetically distinct; they clustered into two well-supported clades in the phylogenetic analyses and two groups in the TCS haplotype network. Moreover, these two groups displayed morphological differences in the dorsal tubercles and radula structure: the trans-Pacific morphotype specimens possess relatively small and dendritic dorsal tubercles, two rows of arborescent tubercles on the dorso-lateral appendages of larger individuals, and radular formula 19-24 ×
The chiton genus Cryptoplax is widely distributed in the Indo-Pacific, extending to southern Australia and the northwestern Pacific (NWP), with 17 recognized species. Among these species, Cryptoplax japonica is commonly found on rocky intertidal and subtidal substrates in the NWP, whereas another species, C. propior, is rarely seen because of its cryptic subtidal habitat and limited distribution. In this study, we surveyed the genetic diversity of C. japonica populations based on 93 individuals from 24 sampling sites along the Korean and Japanese coastlines, including the type locality, using DNA sequences of the mitochondrial gene cytochrome c oxidase subunit I (COI). Haplotype network and phylogenetic analyses of COI sequences revealed two highly divergent genetic lineages of C. japonica separated by a large pairwise genetic distance (10.62%), which was comparable to the genetic difference when either of these two lineages (A or B) is compared with the co-occurring C. propior. In addition to COI sequences, average sequence divergence in 16S rDNA between these three lineages ranged from 2.0 to 3.3%. In contrast to this deep sequence divergence, both morphological examination of radula, girdle and articulamentum colouring, and morphometric analyses of shell measurements using principal component analysis and linear discriminant analysis revealed no diagnostic differences between the two C. japonica lineages. The co-occurrence of these two divergent lineages within most of our studied area, with no morphological differences, indicates cryptic divergence. More extensive sampling from the entire distributional ranges of these cryptic species, in combination with the use of additional molecular markers could shed light on the mechanisms underlying their divergence.
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