This issue sees the publication of the draft genome sequence of an animal that has been studied by biologists for many years as a model for a primitive chordate. The amphioxus or lancelet is a small worm-like creature usually to be found buried in sand on the sea floor. Comparative analysis of the genome of the Florida lancelet, Branchiostoma floridae, reveals 17 ancestral chordate linkage groups conserved in the modern amphioxus and vertebrate genomes despite more than half a billion years of independent evolution. From this it possible to make a virtual reconstruction of the 17 chromosomes of the last common vertebrate ancestor. This reconstruction shows that as suspected, two rounds of whole genome duplication have occurred during evolution of the jawed vertebrate lineage. And it illuminates the murky relationships between the three chordate groups, the tunicates, lancelets and vertebrates.