The homoeo box is a conserved protein-coding DNA sequence present in several genes in arthropods, annelids and vertebrates1–4. Two distinct classes of homoeo box have been identified–the Antennapedia (Antp) class1,5 and the engrailed class6–8. In insects, both classes are found in genes involved in regulating development. We have therefore investigated the phylogenetic distribution of Antp-like homoeo boxes to explore the possibility of a link between their presence and developmental strategy1,9–11. The distribution data also give important insight into the origin of homoeo boxes and the phytogeny of the animal kingdom.