The Comparative Embryology of Sponges
One of the major questions in the evolution of animals is the transition from unicellular to multicellular organization, which resulted in the emergence of Metazoa through a hypothetical Urmetazoa. The Comparative Embryology of Sponges contains abundant o
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Alexander V. Ereskovsky
The Comparative Embryology of Sponges
Alexander V. Ereskovsky Department of Embryology Biological Faculty Saint-Petersburg State University Saint-Petersburg Russia [email protected]
Originally published in Russian by Saint-Petersburg University Press ISBN 978-90-481-8574-0 e-ISBN 978-90-481-8575-7 DOI 10.1007/978-90-481-8575-7 Springer Dordrecht Heidelberg London New York Library of Congress Control Number: 2010922450 © Springer Science+Business Media B.V. 2010 No part of this work may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, microfilming, recording or otherwise, without written permission from the Publisher, with the exception of any material supplied specifically for the purpose of being entered and executed on a computer system, for exclusive use by the purchaser of the work. Printed on acid-free paper Springer is part of Springer Science+Business Media (www.springer.com)
Preface
It is generally assumed that sponges (phylum Porifera) are the most basal metazoans (Kobayashi et al. 1993; Li et al. 1998; Mehl et al. 1998; Kim et al. 1999; Philippe et al. 2009). In this connection sponges are of a great interest for EvoDevo biologists. None of the problems of early evolution of multicellular animals and reconstruction of a natural system of their main phylogenetic clades can be discussed without considering the sponges. These animals possess the extremely low level of tissues organization, and demonstrate extremely low level of processes of gametogenesis, embryogenesis, and metamorphosis. They show also various ways of advancement of these basic mechanisms that allow us to understand processes of establishment of the latter in the early Metazoan evolution. The position of Porifera within the animal kingdom has been problematic since the last decades of the nineteenth century. Due to the limited number of morphological/cytological characteristics, no much conclusive or plausible decision about the phylogenetic position of the sponges could be made. In the literature there were two opposite points of view on position of sponges in the system of Eukaryotes. Some researchers, since Balfour (1879) considered sponges as an independent direction in the evolution of Metazoans, which has arisen irrespective of others (Sollas 1884; Delage 1892; Minchin 1900; Livanov 1955; Hadži 1963; Fedotov 1966; Schulman 1974; Salvini-Plaven 1978; Zhuravleva and Miagkova 1987; Seravin 1997). The opposite point of view belongs to the authors considering the sponges and the true Metazoa as descendants of a common ancestor (Haeckel 1874; Lévi 1956; Beklemishev 1964; Brien 1967c; Brien 1973a; Ivanov 1968, 1971; Tuzet 1970; Hooper et al. 2002; Nielsen 2008). Only the introduction of molecular phylogeny techniques rapidly increased our understanding of evolutionary processes, and definitively confirmed monophyly of Porifera and other Metazoa (Kobayashi et al. 1993; Müller 1997b, 1998; Kim et al. 1999; Lang et al. 2002; Lavrov e
