Extended Data Figure 2. Local arrangement of Hox gene complement in O. bimaculoides and selected bilaterians.

At the top, the four compact Hox clusters of H. sapiens and the single B. floridae cluster are depicted. The D. melanogaster Hox complex is split into two clusters. We included genes in the D. melanogaster locus that are homologues of Hox genes but have lost their homeotic function, such as fushi tarazu (ftz), bicoid, zen and zen2 (the latter three are represented as overlapping boxes). Hox genes in C. teleta are found on three scaffolds¹⁷. L. gigantea has a single cluster with the full known lophotrochozoan gene complement. In O. bimaculoides many of the scaffolds are several hundred kb long, and no two Hox genes are on the same scaffold. The positions of O. bimaculoides genes approximate their locations on scaffolds. Dashed lines indicate that the scaffold continues beyond what is shown. Scaffold length is depicted to scale with size noted on the left. Genes are positioned to illustrate orthology, which is also highlighted by color.