 It was firstly identified in zebrafish and its homologues were also found in sea lamprey and "C. elegans".There are two IL-17Rs (IL-17RA and IL-17RD) in the genome of the basal chordate "Amphioxus".After two rounds of whole genome duplications, these two IL-17R genes expanded into five early vertebrate IL-17R genes, IL-17RA to IL-17RE.