Razor clams, belonging to the Pharidae and Solenidae families, are ecologically and economically important; however, very little research has been conducted on the Pharidae family. The genus Novaculina is a marine-derived freshwater lineage, and Novaculina chinensis is a rare freshwater species of the Pharidae family. In order to understand the phylogenetic relationships of N. chinensis, we sequenced the mitochondrial genome of the genus Novaculina, which is 16,262 bp in length and consists of 12 protein-coding genes (PCGs), 22 transfer RNA genes (tRNAs), and 2 ribosomal RNA genes (rRNAs). The phylogenetic relationships of 69 Imparidentian mitochondrial genomes (mitogenomes) indicated that N. chineisis is closely related to Sinonovacula constricta of the order Adapedonta. Our study also found that the Ka/Ks ratios of 12 protein-coding genes in the Pharidae family are lower than one, indicating the occurrence of negative purification selection. Morphological observations of the siphons of N. chinensis, Novaculina myanmarensis, and Novaculina gangetica indicate that N. chinensis may be the ancestral clade of the genus Novaculina, which has not been proposed in previous studies. Our study provides useful molecular information on the phylogenetic and evolutionary relationships of Pharidae and also contributes to the conservation and management of the germplasm resources of N. chinensis.

Background: Barnacles are important marine fouling organisms, and their complex life cycle involves key metamorphic nodes from nauplius to cyprid larvae and then to sessile adults. However, the molecular mechanisms underlying their larval development remain poorly understood. Metabolomics and transcriptomics are powerful tools for exploring biological development pathways and regulatory networks. Methods: We employed non-targeted metabolomics and transcriptomics to analyze three key developmental stages of embryonic stage, nauplius stage, and cyprid stage. Differential metabolites were screened using fold change (FC), p-value, and variable importance in projection (VIP) values, while DEGs were identified with adjusted p-value and |log₂(fold change)| criteria. WGCNA was used to construct gene co-expression networks, and qRT-PCR validated RNA-seq results. Results: A total of 3683 metabolites were identified, with the bile secretion pathway serving as a core regulatory pathway throughout early development. Transcriptomic analysis identified 7234 DEGs, which were clustered into four modules corresponding to different developmental stages. Key pathways such as chitin metabolism, and linoleic acid metabolism were significantly enriched, and qRT-PCR confirmed the reliability of RNA-seq data. Conclusions: This study reveals the metabolic and molecular regulatory mechanisms underlying the early development of M. volcano, highlighting stage-specific metabolic characteristics and core gene modules. The findings provide a theoretical basis for understanding barnacle developmental adaptation strategies and offer potential targets for the development of novel antifouling agents.