The razor clam genus Novaculina is a secondary marine-derived freshwater taxa within the otherwise exclusively marine family Pharidae. Novaculina currently comprises four valid species that are distributed allopatrically across several drainages in Asia. 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 recognised congeners. Furthermore, morphological examination reveals distinct characteristics in 'N. siamensis', namely a fused, fringed siphon, in contrast to the separated, 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 in having a short shell, deep pallial sinus, elongate, oval to bean-shaped anterior adductor scar and long fused siphons surrounded by conical tentacles. [ABSTRACT FROM AUTHOR]