Evolution of the ParaHox gene cluster and relative expression domains in bilateral animals. Schematic representation of ParaHox genomic organization and expression patterns in several bilateral animals: the mouse Mus musculus [9, 17, 23, 33, 63], the bowfin fish Amia calva , the hagfish Eptatretus burgeri , the lancelet Branchiostoma floridae [5, 11], the sea urchin Strongylocentrotus purpuratus [7, 19], the sea star Patiria miniata (present study) and the polychaete Platynereis dumerilii . Arrows indicate ParaHox genes and their orientation in the genome; a continuous line below arrows indicates an intact cluster. The cartoons on the right side of the panel schematize the domains of expression of ParaHox genes in representatives of some of the bilaterian groups. Mouse, amphioxus, sea urchin and sea star embryos are in lateral view; the polychaete embryo is in frontal view. Nervous system domains are depicted with dashed lines. Endodermal structures are in gray. Gsx expression is shown in blue, Xlox in green and Cdx in magenta. Amphioxus Gsx expression in the hindbrain is depicted in light blue, as at the stage of development represented here, this domain of expression is fading out . kb, kilobases; Chr, chromosome. Double-parallel lines indicate long genomic distance.