Fig. 1

Phylogenetic analysis of the Sycon bHLH proteins. An unrooted maximum likelihood (ML) tree is shown. This tree has been constructed using the bHLH domains from Sycon ciliatum and Amphimedon queenslandica (sponges), Trichoplax adhaerens (placozoans), Nematostella vectensis, Hydra magnipapillata and Acropora digitifera (cnidarians), Drosophila melanogaster and Daphnia pulex (bilaterians, arthropods), Lottia gigantea (bilaterians, molluscs), Capitella teleta (bilaterians, annelids), and Homo sapiens (bilaterians, chordates). Several monophyletic groups are found and are named according to previous studies [4, 14, 15]. The Atonal-related group [4] is also indicated. We listed in the figure the proteins from Sycon ciliatum (Sci) and Amphimedon queenslandica (Aqu). The robustness of the nodes that define the different monophyletic groups was assessed by evaluating their statistical supports in the ML analysis. This is represented on the tree by the presence close to the name of the group of *** (aLRT and aBayes values > 0.95), ** (0.95 > aLRT and aBayes values > 0.8), or * (aLRT and aBayes values < 0.8)