ORIGINS OF THE ECHINOZOAN BODY PLAN

Echinozoans, the group of animals including echinoids (sea urchins) and holothurians (sea cucumbers) is a diverse clade occupying a range of ecologies and habitats in today’s oceans. Modern echinozoans occupy a disparate range of body plans, from the soft-bodied vermiform holothurians, to the multi-plated globular echinoids. Echinozoans are first known from the Ordovician period, and despite their well-characterized body plans in modern ecosystems, little is known of the morphological characterization of their earliest representatives. To better understand the this, we used a multilevel approach that combines paleontological, genomic, and developmental data. We first carried out micro-CT scanning of various basal taxa, which clarifies the morphological transitions characterizing the early evolution of their body plans. We then constructed a character matrix encompassing numerous Paleozoic echinozoans, along with other echinoderm outgroups, to understand the inter-relationships of echinozoan classes, and their relationships to other eleutherozoans (including asteroids, ophiuroids, and edrioasteroids). We then analyzed changes in disparity leading from their earliest members, up to those of the crown group. Finally, to understand the genomic underpinning of the morphological changes that characterize echinozoan bodyplans, we carried out analyses of gene content from genomes and transcriptomes of extant species, to understand sources of genomic novelty, and analyzed the expression of key genes involved in the development of the their body plans. This sheds new light on the origin of the echinozoan body plan from paleontological, genomic, and developmental perspectives.