Abstract

Comparative ontogenetic studies have long been used to infer evolutionary pathways and animal interrelationships and have resulted in a number of iconic hypotheses such as Haeckel’s biogenetic law or Hatschek’s trochozoan concept. This is because most metazoans often display so-called transient characters that are lost during subsequent development and hence are not recognizable in the adult. However, organisms constitute the sum of their characters displayed over their entire lifetime, and thus every character displayed during any stage of development belongs to an animal’s “body plan“, irrespective of whether the character itself is retained through adulthood or not. Accordingly, ontogenetic studies may provide an important window into the evolutionary past of animals, a quality they only share with findings revealed from the fossil record. With the rise of molecular biology, applications such as in situ hybridization, experimental genetics, as well as genomics, comparative transcriptomics, and single cell RNAseq, studies into morphogenesis can now be supplemented by fine-grained molecular data in order to reveal the underlying genetic mechanisms that govern animal ontogeny and evolution. The present talk aims at reconstructing the evolutionary history of one of the most diverse and species-rich animal phyla, Mollusca, by combining data from the fossil record, morphogenesis, and evodevo including transcriptomics, phylogenomics, and single cell RNA seq. I will also highlight how ancient molecular components and pathways have been integrated into the ontogeny of different metazoan taxa, and have thereby significantly contributed to the diversity of developmental modes and animal life forms on our planet.