Chapter 9 - The extent of Ctenophore uniqueness—distinctly recognized to be “quasi-Cnidarians” or “stunted Bilaterians”

Abstract

The age dating analysis of Eoandromeda, the prehistoric Ctenophore, ascertained that the origin and evolution of Sea gooseberries or Ctenophores happened in the pre-Cambrian and Cambrian period around 580–551mya, whereas the molecular data of ribosomal RNA made the molecular phylogeneticists to contemplate Ctenophores as the sister group of all Metazoans (Chen et al., 2007; Tang et al., 2011). The earliest fossil record of Porifera along with the contemporary molecular phylogenetic analysis revealed that sponges have evolved around 540–548mya in the pre-Cambrian period (Penny et al., 2014). In Metazoans, the lack of epithelial, nervous, and muscular tissue system in Porifera; its presence in Cnidaria and Bilaterians; and the existence of an incipient nervous system in Ctenophora rendered the scientists to hypothesize that the evolution of nervous systems in Cnidarians/Bilaterians and evolution of the primitive nervous systems in Ctenophores, happened twice, independently (Telford et al., 2016; Moorhead, 2019).