Fig. 6

Phylogenetic classification of metazoan globins. a Table of the clades suggested in this study. The current name column indicates the denominations used in previous literature. b Table of the number of genes of each clade present in the species genome we sampled. For clade I, the number of extracellular globins is indicated between parentheses. An asterisk shows all the species in which HBL-Hb linker proteins have been detected. Interrogation marks indicate missing data because the whole genome is not available for the relevant species. On the right, the animal tree shows the inferences of gain and loss of globin gene clades in key metazoan ancestors. Colored disks indicate the gain of a new gene clade by duplication from existing ancestral genes while crossed disks illustrate the numerous secondary losses of globin clades. The green circles with a question mark illustrate the uncertainty on the appearance of a clade III gene in metazoan ancestors, as some cnidarians and a ctenophore possess genes with possible clade III affinities (Additional file 8). In the deuterostome branch, the extinction of clade III (green circle with a cross) occurred independently in Branchiostoma, Ciona and Homo lineages because clade III genes (globin X) have been identified in several vertebrate species [40]