Tapetinae

Species of Tapetinae seem to evolve more rapidly than other subfamilies in Veneridae, either from the less conservative gene arrangement or from the higher transversion divergence rate in 16S (Canapa et al., 1996). Moreover, the homogeneously morphological characters led to misidentification and unreasonable phylogenetic inference by Chen et al. (2011b). In our study, the genus Marcia is polyphyletic: Marcia hiantina and Marcia japonica (Gmelin, 1791) cluster with Tapes Megerle von Mühlfeld, 1811 in both trees, whereas Marcia recens (Holten, 1802) clusters with Paphia in the CB tree and with Ruditapes decussatus (Linnaeus, 1758) in the MT tree (Fig. 4). This result indicates that Marcia hiantina and Marcia japonica have a closer relationship to Tapes, which is consistently supported by the mitochondrial gene arrangement. In addition, we confirmed two shell forms of Marcia hiantina (Fig. 8), of which one (type B) is similar to Tapes. As a result, we here suggest that Marcia hiantina and Marcia japonica should be reassigned to the genus Tapes, and rename them as Tapes hiantina comb. nov. and Tapes japonica comb. nov.

The placement of Irus in the topology based on multigene fragments failed to support the monophyly of Tapetinae (Fig. 4B). Considering the differences in phylogenetic trees based on short gene fragments and mitogenomes in Venerinae and Dosiniinae, the genus Irus should remain in Tapetinae until further molecular evidence, such as whole mitochondrial sequences, is available. Two Irus sequences, obtained from the studies by Mikkelsen et al. (2006) and Goto et al. (2012), are significantly different from other newly collected Irus species in clade A7. The absence of available sample photographs cannot rule out the possibility of an error in identification. In particular, there are significant morphological differences between Irus crenatus and other Irus species according to Mikkelsen et al. (2006).

Furthermore, the features and mitogene arrangements of three Ruditapes species, Ruditapes aspera Quoy & Gaimard, 1835, Ruditapes decussatus and Ruditapes philippinarum, do not exhibit a high degree of similarity, and none of these species has a sister-group relationship. Consequently, these three species might belong to three different genera (Liu et al., 2022).