Fig. 1

Families from bHLH group A (to which belong most of the so-called “neurogenic” bHLH genes) present in different species from several animal clades. The orthologs’ genes involved in other metazoans neurogenesis and identified in Xenacoelomorpha are indicated with an orange dot. Colored boxes indicate the presence of the family in that species, while empty boxes indicate their absence. The families from Xenacoelomorpha species are showed with in green. Question marks inside boxes represent the presence of a family member in need of further confirmation (additional gene features). The two last columns represent the number of orphans and the total number of bHLH genes in each selected species (not only from group A). The image allows us to identify the losses produced in the different clades over evolutionary time. The families present in our different species would support the idea of a bHLH gene expansion between the cnidarian and nephrozoan divergence (clearly seen in the group A), as suggested by other authors [25]. Many families have bilaterian, but not cnidarian members; several of them are found in the X. bocki’s genome (see also, Fig. 2). The data for X. bocki and S. roscoffensis are derived from our previous analysis [11]. Reference species used here are: H. sapiens, N. vectensis, Daphnia pulex, Caenorhabditis elegans, Tribolium castaneum, Lottia gigantean, Branchiostoma floridae, Amphimedon queenslandica, Strongylocentrotus purpuratus, Capitella sp. I., D. melanogaster and H. magnipapillata, all derived from the study of [25]; the data of Schmidtea mediterranea was from [33]; the data from A. digitifera (plus the latest identifications in N. vectensis) and Trichoplax adhaerens were obtained from [32, 34]; the Sycon ciliatum data were from [35]