Article Addendum

Bernd Schierwater,1,2,* Sergios-Orestis Kolokotronis,2 Michael Eitel1 and Rob DeSalle2,* 

The Diploblast-Bilateria Sister hypothesis
Parallel evolution of a nervous systems may have been a simple step

1) ITZ; Ecology and Evolution; Tierärztliche Hochschule Hannover; Hannover, Germany;
2) ackler Institute for Comparative Genomics, American Museum of Natural History;
New York, NY USA

 [Communicative & Integrative Biology 2:5, 1-3; September/October 2009]; ©2009 Landes Bioscience
 

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Abstract

For many familiar with metazoan relationships and body plans,
the hypothesis of a sister group relationship between Diploblasta
and Bilateria1 comes as a surprise. One of the consequences of
this hypothesis—the independent evolution of a nervous system
in Coelenterata and Bilateria—seems highly unlikely to many.
However, to a small number of scientists working on Metazoa,
the parallel evolution of the nervous system is not surprising
at all and rather a confirmation of old morphological and new
genetic knowledge.2-4 The controversial hypothesis that the
Diploblasta and Bilateria are sister taxa is, therefore, tantamount
to reconciling the parallel evolution of the nervous system in
Coelenterata and Bilateria. In this addendum to Schierwater
et al.1 we discuss two aspects critical to the controversy. First
we discuss the strength of the inference of the proposed sister
relationship of Diploblasta and Bilateria and second we discuss
the implications for the evolution of nerve cells and nervous
systems.

Key words: placozoa, trichoplax, urmetazoon hypothesis, basal metazoan evolution, trichoplax.com, pre-nervous system, placula
hypothesis