The XVIIIth (New) International Congress of Zoology

Le XVIIIème (Nouveau) Congrès International de Zoologie

In this paper I will review models proposed in the literature for the transition of the phenotype from uni-to multicellular animals (eg. from ciliates to acoels, from choanoflagellates to the "Phagocytella", from flagellates to the "Gastrea", from flagellates to the "Planuloid", and from flagellates to the "Gallertoid"). The paper will specify the differences between early cell colonies and the first body plans of true multicellular animals (eg. Choanoflagellida and Volvocales versus Placozoa, Parazoa and "Coelenterata"). In addition, the paper will place emphasis on the significance of asexual reproduction and colonial organisation during the early phases of metazoan evolution. The significance of the extracellular matrix (ECM) and of the monociliated cell as plesiomorphic features of the metazoan body plan will be addressed. In addition, early strategies in feeding and in life styles, which may have influenced the design of early metazoans, as well as the importance of a biphasic life cycle with a microscopic larva and a macroscopic adult will be discussed. Reference: R. Rieger and S. Weyrer 1998: The Evolution of the lower Metazoa: Evidence from the phenotype in W.E.G. Müller, Progress in Molecular and Subcellular Biology, Vol. 21