title: Where is my mind? How sponges and placozoans may have lost neural cell types.
abstract: Recent phylogenomic evidence suggests that ctenophores may be the sister group to the rest of animals. This phylogenetic arrangement opens the possibility that sponges and placozoans could have lost neural cell types or that the ctenophore nervous system evolved independently. We critically review evidence to date that has been put forth in support of independent evolution of neural cell types in ctenophores. We observe a reluctance in the literature to consider a lost nervous system in sponges and placozoans and suggest that this may be due to historical bias and the commonly misconstrued concept of animal complexity. In support of the idea of loss (or modification beyond recognition), we provide hypothetical scenarios to show how sponges and placozoans may have benefitted from the loss and/or modification of their neural cell types.
authors.affiliation: Whitney Laboratory for Marine Bioscience, University of Florida, 9505 Ocean Shore Blvd, St Augustine, FL 32080, USA Department of Biology, University of Florida, Gainesville, FL 32611, USA joseph.ryan@whitney.ufl.edu.
authors.forename: Joseph F
authors.initials: JF
authors.lastname: Ryan
authors.affiliation: Whitney Laboratory for Marine Bioscience, University of Florida, 9505 Ocean Shore Blvd, St Augustine, FL 32080, USA Department of Biology, University of Florida, Gainesville, FL 32611, USA.
authors.forename: Marta
authors.initials: M
authors.lastname: Chiodin
mesh_terms: D000818:Animals; D005075:Biological Evolution; D009420:Nervous System; D009474:Neurons / Q000502:physiology*; D054909:Placozoa / Q000166:cytology*; D011161:Porifera / Q000166:cytology*
keywords: Ctenophora; Placozoa; Porifera; animal evolution; loss; nervous system