Venerinae

Liu, Yumeng, Ma, Peizhen, Zhang, Zhen, Li, Cui, Chen, Ya, Wang, Yunan & Wang, Haiyan, 2022, The new phylogenetic relationships in Veneridae (Bivalvia: Venerida), Zoological Journal of the Linnean Society 196, pp. 346-365 : 357

Venerinae

Dall (1902) proposed Anomalodiscus as a section of Anomalocardia Schumacher, 1817 , but the taxonomy of these genera has always been controversial ( Jukes-Browne, 1914; Prashad, 1932; Habe, 1977). Anomalodiscus is usually considered monotypic, containing only one species, Anomalodiscus aquamosus (Linnaeus, 1758) ( Fischer-Piette & Vukadinovic, 1977; Zhuang, 2001; Huber, 2010). In the CB tree ( Fig. 4A ), Anomalodiscus squamosus forms a highly supported monophyletic group with Timoclea . We then took Timoclea scabra (Hanley, 1845) as a representative of Timoclea and compared its characteristics with Anomalodiscus aquamosus . The results show that both species share similar hinges and sculptures, which are key characteristics in Anomalodiscus ( Dall, 1902; Fig. 7A–C, E–G ). Meanwhile, fluted crenulations on the margin of the inner surface of the shell are observed in both species ( Fig. 7D, H ). Therefore, both molecular and morphological evidence supports the placement of Anomalodiscus squamosus in Timoclea and the monotypic genus Anomalodiscus as a subgenus of Timoclea .

Periglypta Jukes-Browne, 1914 has long been a controversial genus in Venerinae, concerning validity and subfamily assignment. Huber (2010) considered that the distinction between Antigona and Periglypta was questionable and indicated a morphological continuum from Antigona lamellaris Schumacher, 1817 to Periglypta puerpera if all known global Antigona and Periglypta species are considered. Accordingly, Periglypta has been proposed as a synonym for Antigona ( Huber, 2010) . Despite the lack of distinguishing characters, the typical species of both genera, Antigona lamellaris and Periglypta puerpera , do not cluster together in either the CB or MT tree. In addition, tRNAs in the mitogenomes of the two species appear to have a large span translation, demonstrating that Antigona and Periglypta are two distinct genera.

Subfamily placement of Periglypta remains a matter of debate. Although typical Venerinae characters were found in Periglypta ( Kappner, 2006) , its position varied depending on molecular markers used in previous phylogenetic studies ( Kappner & Bieler, 2006; Mikkelsen et al., 2006; Chen et al., 2011b). The placement of Periglypta remains unresolved in the tree topology based on multigene fragments, but highly resolved in the mitogenome-based topology. Within the MT tree, Periglypta puerpera clusters with Venerinae and forms a clade ( Fig. 4C ). Gene arrangements provide powerful evidence for the taxonomic status of Periglypta . A complex, derived arrangement shared by taxa is a convincing indicator of relatedness and is unlikely to have arisen independently in separate lineages ( Boore & Brown, 1998). Periglypta puerpera shares a longer gene chain with Venerinae than species from other subfamilies ( Fig. 6A ). Consequently, we suggest the placement of Periglypta in Venerinae.

Figures

Figure 4. Phylogram of clade A.A, phylogram of clades A1–A4 from Figure 3. B, phylogram of clade A from Figure 3, except for clades A1–A4. C, phylogram of clade A from Figure 2.

Figure 6. Gene arrangements of mitogenomes in venerids. A, gene arrangements in Venerinae, Chioninae, Dosiniinae and Gouldiinae. B, gene arrangements of species from different subfamilies sharing the same order of protein-coding genes.

Figure 7. Shell of Anomalodiscus squamosus (A–D) and Timoclea scarbra (E–H). A, E, external view of left valve and internal view of right valve. B, F, sculpture. C, G, hinge. D, H, fluted crenulations.