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Molecular phylogeny reveals Cenonovaculina gen. nov. (Adapedonta: Pharidae), a new freshwater razor clam genus from Indochina

Ekachai Jeratthitikul , Chirasak Sutcharit

Abstract

The razor clam genus Novaculina is one of the secondary marine-derived freshwater taxa within the otherwise exclusively marine family Pharidae. It currently comprises four valid species that are distributed allopatrically across several drainages in Asia. In this study, we employed an integrated approach, combining morphology and molecular phylogenetic analyses, to elucidate the taxonomic placement of members within this genus. The multi-locus phylogenetic trees based on cytochrome c oxidase subunit I (COI), 16S rRNA and 28S rRNA gene sequences demonstrate that Novaculina is polyphyletic. Specimens identified as N. siamensis form a distinct clade that is not sister group to other currently recognized congeners. Furthermore, morphological examination reveals distinct characteristics in ‘N. siamensis’, namely a fused and fringed siphon, in contrast to the separated and smooth siphons observed in other species. Based on these findings, we propose the establishment of a new genus, Cenonovaculina gen. nov., to accommodate 'N. siamensis'. The new genus is distinguished from other genera by having a relatively short shell, a deep pallial sinus, an elongate oval to bean-shaped anterior adductor scar, and long fused siphons surrounded by conical tentacles.

IS24024  Accepted 28 March 2024

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