Eukaryotic phylogeny and the appearance of ECM proteins. The figure diagrams the major taxonomic divisions of eukaryotes (Box 1), and is based on published phylogenetic analyses (e.g., Philippe et al., 2005, 2009; Shalchian-Tabrizi et al., 2008; Pick et al., 2010) as well as on analyses of whole genome sequences (see main text). Taxa for which whole genome sequences are available are marked with asterisks. The diagram represents topologies of relationships, and the branch lengths are not intended to reflect accurate evolutionary distances. The relationships of apusomonads and placozoa are not well defined; their placement in the diagram is influenced in part by evidence from analyses of ECM-related genes (see main text). Taxa with the complement of ECM proteins typical of all bilateria are within the light blue hexagon. Taxa highlighted with green or blue text have some homologues of bilaterian ECM proteins or their receptors (see main text), but lack a complete set. The complexity of the known ECM protein sets in these organisms increases from left to right. In contrast, the taxa within the gray trapezoid show no evidence of any credible examples of metazoan ECM proteins. First known appearances of relevant genes/proteins or domains are marked in red. Note that taxa appearing to the right of (i.e., subsequent to) the origin of a given feature may have lost it; examples would be the absence of integrins in choanoflagellates sequenced to date and the absence of fibrillar collagens in Drosophila (in both cases, presumably by gene loss).