Geographic Distribution and Genetic Structures of the Tideland Snails Pirenella nipponica and P.asiatica in Taiwan and Japan.

The tideland snails Pirenellanipponica and Pirenellaasiatica are distributed north of the central Ryukyu Islands and in South Ryukyu, respectively, in Japan. To reveal their distribution and genetic characteristics in Taiwan, we sampled Pirenella snails along the western coast of Taiwan Island and analyzed the nucleotide sequences of their mitochondrial DNAs. Pirenella nipponica and P. asiatica inhabit the northern and southern parts of the western coast of Taiwan, respectively, and coexist only in the central part. Taiwanese and Japanese populations of P. asiatica showed significant genetic differentiation. The former showed higher genetic diversity and a larger effective population size than the latter. However, the Taiwanese population of P. nipponica was not genetically deviated from the local Japanese population on Kyushu Island. Both the Taiwan and Kyushu populations of P. nipponica showed significant genetic differences from local populations in other regions of Japan, namely, Honshu Island (the Japanese mainland) and Central Ryukyu. They also showed higher genetic diversity and a larger effective population size than the others. The Taiwanese populations of both species might be part of a large panmictic population with individuals from the Asian continent and Kyushu Island.

The mitochondrial genome of the threatened tideland snail Pirenella pupiformis (Mollusca: Caenogastropoda: Potamididae) determined by shotgun sequencing.

The nearly complete mitochondrial genome of the threatened tideland snail Pirenella pupiformis (Mollusca: Cerithioidea: Potamididae) was determined by shotgun next-generation sequencing. The mitogenome is comprised of 13 protein-coding genes (PCGs), two ribosomal RNA (12S and 16S) genes, and 22 transfer RNA genes (tRNAs). This gene order is consistent with the previously published mitochondrial genomes of other species belonging to the family Potamididae. The family Potamididae including P. pupiformis was recovered as a monophyletic group in the superfamily Cerithioidea.

Snails associated with the coral-killing sponge Terpios hoshinota in Okinawa Island, Japan.

Terpios hoshinota is a thin encrusting sponge that overgrows live scleractinian corals and it is linked to coral loss in many reefs. However, our knowledge of the species associated with this sponge species is poor. During a periodical survey of T. hoshinota in 2020, we found tiny snails crawling on the sponge in the subtropical waters around Okinawa Island, Japan. We observed egg capsules inside the sponge tissue and veliger larvae released from the egg capsules. Molecular analyses of both the snails and veliger larvae (cytochrome oxidase I, COI) showed that they were identical and belonged to Joculator sp. (family Cerithiopsidae). There was no direct observation of predation on the sponge by this snail; however, to the best of our knowledge, this is the first report on a close association between a snail and the sponge T. hoshinota.

The mitochondrial genome and phylogenetic position of a marine snail Nerita (Heminerita) japonica (Gastropoda: Neritimorpha: Neritidae).

The mitochondrial genome of the neritid snail Nerita (Heminerita) japonica (Mollusca: Neritimorpha) from Kumamoto, Japan was determined by whole-genome sequencing. This mitogenome is comprised of 13 protein-coding genes, 2 ribosomal RNA (12S and 16S) genes, and 22 transfer RNA genes, with the same gene order as in the other species of the family Neritidae. A likelihood-based phylogenetic reconstruction recovered the subgenus Heminerita (including N. japonica as its type and N. yoldii from China) as monophyletic and sister to a clade with four species of the subgenera Nerita and Theliostyla.

The mitochondrial genome of the gold-ringed cowry Monetaria annulus (Mollusca: Gastropoda: Cypraeidae) determined by whole-genome sequencing.

The mitochondrial genome of the cowry snail Monetaria annulus (Caenogastropoda: Cypraeoidea: Cypraeidae) was determined by whole-genome next-generation sequencing. The mitogenome is composed of 13 protein-coding genes (PCGs), 2 ribosomal RNA (12S and 16S) genes, and 22 transfer RNA genes (tRNAs). This gene order is consistent with the previously published mitochondrial genomes of other species belonging to the order Littorinimorpha. The superfamily Cypraeoidea was recovered as a sister clade to the group of Tonnoidea and Neogastropoda.

The complete mitochondrial genome of the stream snail Clithon retropictus (Neritimorpha: Neritidae).

The complete mitochondrial genome of the stream neritid Clithon retropictus was determined by next-generation sequencing. The mitochondrial genome is 15,814 bp in length, comprising two ribosomal RNA genes, 13 protein-coding genes (PCGs) and 22 transfer RNA genes (tRNAs). Of these 37 genes identified, 7 PCGs and 8 tRNAs are encoded on the heavy strand and the other genes on the light strand. This gene order is consistent with the previously published mitochondrial genomes of the other neritid species. This is the first report of a complete mitochondrial genome sequence for the genus and the fourth for the gastropod subclass Neritimorpha.