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Introduction: Sea slater, in the genus Ligia, is widespread in rocky shore habitats, and the taxon is easily isolated due to its limited dispersal capacity. Therefore, most Ligia species exhibit an allopatric distribution, but Ligia exotica and L. cinerascens exhibit an overlapping distribution distribution in East Asia. Previous studies on both species have confirmed the existence of highly divergent lineages based on 16S rRNA. Methods: In the present study, 282 Ligia individuals were collected at ten, three, and three sites in South Korea, Japan, and Vietnam, respectively, and 41 haplotypes were observed based on 16S rRNA. Results and discussion: The results of phylogeny, phylogenetic network, and TCS network, Principal Coordinates Analysis, and four Molecular Species Delimitation Analyses revealed that six genetic lineages including L. cinerascens, LineagesNand S of L. exotica, Ligia sp. 1, sp.2 and sp.3 were present. The three genetic lineages, including L. cinerascens, Lineage N of L. exotica, and Lineage S of L. exotica, were also identified in the phylogeny based on a nuclear gene of the sodium-potassium ATPase α-subunit (Nak). Phylogeographic analysis revealed that L. cinerascens and Lineage N of L. exotica were distributed overlappingly in South Korea, Japan, and the northern region of China. Generally, the two lineages of L. exotica were distributed allopatrically, which was more evident along the coastline of mainland China than that of Japan. The results of time-calibrated phylogeny suggested that the speciation events of Ligia species might be associated with Japanese mainland formation from Oligocene to Miocene (approximately 30-5 million years ago, Mya). The results of the present study provide insights that could facilitate the understanding of the evolutionary history of Ligia, tracking of geological processes, and evolutionary effects of palaeogeographical events at the population level. [ABSTRACT FROM AUTHOR]

A giant water bug Lethocerus deyrollei (Hemiptera: Belostomatidae) is a large, predatory, and nocturnal hemipteran insect, which has been considered threatened and thus enrolled as an endangered species in South Korea and Japan. Here, we characterized the complete mitochondrial genome of L. deyrollei, which has a circular form with 19,295bp in length, which is the longest when compared to those of the 111 hemipteran species reported so far. Its longest genome size is due to the extremely extended CR (4686bp), which is much longer than those of China and Japan. It consisted of a total of 37 genes (13 PCGs, 22 tRNA genes, and two rRNA genes) and one control region (CR). The genome composition and gene order were identical to those previously reported from the same species of China and Japan with over 99.7% sequence similarities except for CR and trnI. The nucleotide composition was highly AþT biased, accounting for 71% of the whole mitochondrial genome, as in other species of Nepoidea. Based on the aa sequences of 13 PCGs, we reconstructed a maximum likelihood tree, which indicated that the three mitochondrial genomes of L. deyrollei from South Korea, China, and Japan are grouped, and also Lethocerus, Belostomatidae, Nepoidea, Nepomorpha, Heteroptra are strong monophyletic groups, respectively. [ABSTRACT FROM AUTHOR]