We identified five putative vasotocin receptor genes in the jawless sea lamprey.
Tissue expression patterns reveal homologies with jawed vertebrate orthologs.
Phylogeny indicates three V1/oxytocin-clade receptors, a V2B and a V2C receptor.
Each of two paralogous lamprey scaffolds contains a pair of syntenic V1–V2 genes.
Synteny analysis supports a shared one-round whole-genome duplication scenario.