Evolutionary history of the calcium-regulated photoprotein family. According to currently available sequence data, the family arose at the base of the Metazoa. Filled blue circles indicate that the genes are present and that bioluminescence is observed in these groups. Open blue circles indicate that the genes are present, but that bioluminescence is not observed in these groups. A brown X indicates that photoprotein genes are absent from those groups. A plus sign next to a taxon name indicates that this organism's genome has been fully sequenced.