Molecular phylogeny of Nipponacmea (Patellogastropoda, Lottiidae) from Japan: a re-evaluation of species taxonomy and morphological diagnosis

The patellogastropod limpet genus Nipponacmea is widely distributed in Japan and adjacent East Asia. Species identification within Nipponacmea is challenging due to the high variation in shell morphology. In this study, we examined the taxonomy of this genus represented by nine nominal species from 43 localities (including type localities). Results of the molecular phylogenetic analysis revealed that: (1) N.gloriosa, the sole species in this genus inhabiting the subtidal zone, represents the most basal independent branch; (2) the remaining species are divided into two large clades with lower- and higher-apex shell profiles; and (3) the high-apex morphology was derived from the low-apex type. The terminal clades defined using the molecular data were consistent with nine morphospecies and had 100% bootstrap values, strongly supporting the conventional taxonomy of Nipponacmea. Although morphological similarities do not always reflect phylogeny, the set of morphological characters used in the current taxonomy were proven to be adequate for diagnosis. In conclusion, this study provided solid evidence to uphold the monophyly of known species of Nipponacmea in Japan and demonstrated the usefulness of morphological characters for species diagnosis.

Evolutionary lineages of marine snails identified using molecular phylogenetics and geometric morphometric analysis of shells

The relationship between morphology and inheritance is of perennial interest in evolutionary biology and palaeontology. Using three marine snail genera Penion, Antarctoneptunea and Kelletia, we investigate whether systematics based on shell morphology accurately reflect evolutionary lineages indicated by molecular phylogenetics. Members of these gastropod genera have been a taxonomic challenge due to substantial variation in shell morphology, conservative radular and soft tissue morphology, few known ecological differences, and geographical overlap between numerous species. Sampling all sixteen putative taxa identified across the three genera, we infer mitochondrial and nuclear ribosomal DNA phylogenetic relationships within the group, and compare this to variation in adult shell shape and size. Results of phylogenetic analysis indicate that each genus is monophyletic, although the status of some phylogenetically derived and likely more recently evolved taxa within Penion is uncertain. The recently described species P. lineatus is supported by genetic evidence. Morphology, captured using geometric morphometric analysis, distinguishes the genera and matches the molecular phylogeny, although using the same dataset, species and phylogenetic subclades are not identified with high accuracy. Overall, despite abundant variation, we find that shell morphology accurately reflects genus-level classification and the corresponding deep phylogenetic splits identified in this group of marine snails.

A putative species complex in the Sea of Japan revealed by DNA sequence data: a study on Lottia cf. kogamogai (Gastropoda: Patellogastropoda)

A putative new limpet species (Patellogastropoda) from the Sea of Japan is revealed by molecular genetic analyses using the mitochondrial markers 16S rRNA and cytochrome c oxidase subunit I (CO1), as well as the DNA marker 18S rRNA. Our data indicate that the limpet, collected in the Peter the Great Bay (Russian Federation), is not, as its morphology suggests, the Japanese species Lottia kogamogai Sasaki and Okutani, 1994, and might also hint towards another putative species complex in the Sea of Japan. The different currents between the Far East Asian mainland (cold, subpolar jet running southwards) and the Japanese archipelago (warm, subtropical jet running northwards) are likely to act as a barrier that has a substantial influence on species distribution in these waters. Accordingly, our results indicate that it is about time for a revision of patellogastropod species with a reported distribution in Japanese and Far Eastern Russian waters by an integrative approach using molecular genetic and morphological characters. The species investigated herein is referred to as Lottia cf. kogamogai until it is morphologically re-examined and compared with primary type specimens of known species.