True sea snakes (Hydrophiini) are among the few extant reptiles to exhibit secondary adaptation to a marine environment, and have developed a unique set of associated physiological characteristics. One such adaptation is the ability to respire through their skin by intaking oxygen and expelling carbon dioxide and sea snakes are able to perform this gas exchange process at much lower pressures and temperatures than industrial gas separation techniques. Our goal is to investigate the genetic basis of this unique adaptation. To do so, we have generated chromosome-scale assemblies for two Hydrophiini, namely Hydrophis curtus and Hydrophis ornatus, using a combination of ultra-long Oxford Nanopore and highly accurate Illumina short-read  sequencing and Hi-C proximity sequencing. For each sea snake we have generated ~2 Gb genomes with 7 macrochromosomes and ~10 microchromosomes, consistent with the known karyotype for these species. These assemblies show excellent contiguity, accuracy and completeness, with scaffold N50s of ~270 Mb and 91% complete single-copy BUSCOs. We are using these assemblies to annotate the sea snake transcriptome and investigate respiration genes. We are also comparing their genomes to that of terrestrial snakes to better identify regions associated with aquatic adaptation. This will provide a resource to begin investigating the genetic architecture of tetrapod marine adaptation.