A main challenge of animal evolutionary genomics and evo-devo is to identify how bilaterian hallmarks emerged. The available non-bilaterian genomes evidenced that the ancestral animal genome contained a diversified developmental toolkit, including building blocks required for bilaterian body plans. Accessing animal genome diversity is needed to understand which genomic changes contribute to which phenotypic changes. As glass sponges differ from the three other sponge classes in development, tissue and physiology, sequencing the genome of an Hexactinellida and its symbiont appears evolutionary relevant.