Addressing distributional and taxonomic uncertainty in the deep-sea giant isopod genus Bathynomus with an integrated observational and molecular framework

Although the deep sea ( > 200 m) represents most of the ocean’s habitat, biodiversity baselines remain poorly resolved due to fragmented records and taxonomic uncertainty among morphologically similar and cryptic taxa. The deep-sea isopod genus Bathynomus exemplifies this problem, where unresolved species identities and sparse molecular references limit interpretation of distributional patterns. To systematically resolve sporadic historical Bathynomus identifications, we assembled and standardized a global occurrence database from public archives such as the Global Biodiversity Information Facility (GBIF) and digitized literature, implemented automated data-integrity checks (e.g., inland coordinates, aquarium records, published misidentifications and unverified descriptions), and linked records to available mitochondrial barcodes within a relational database. To demonstrate molecular analyses, we conducted trap-based surveys in the Bahamas and Japan to obtain 102 specimens and recover high-quality tissue for sequencing and phylogenetic placement. We collected 15,564 georeferenced records from 1,994 sampling events, including 689 observations linked to mitochondrial barcodes, and supported the hypothesis that verified species taxa do not span multiple ocean basins. We reconstructed and annotated the first B. giganteus mitochondrial genome (14,968 bp) and evaluated genetic distances to validate specimen identity. Uneven spatial sampling effort and limited mitochondrial markers for congeners continue to challenge Bathynomus research, demonstrating the need for expanded standardized sampling and improved barcode references.