Animal Evolution: Interrelationships of the Living Phyla . Second Edition by ClausNielsen . New York : Oxford University Press, Inc. , 2001 . x + 563 pp. Line drawings. Paperback . ISBN-13 958 0198506829 .

The manuscript of the first edition of Nielsen’s book, published in 1995, was actually finished in 1992. This explains why the author had already started preparing a new edition when the first was still hot from the press. The author has been thus able to revise his work thoroughly in a relatively short time span. In this new edition, one reference out of four is from the 1995–99 literature, with a few papers as recent as 2000. But Nielsen’s revised ‘magnum opus’ has not simply been one of adding new data here and there – incidentally, causing the book to swell by hundred additional pages. He has been able indeed to revise his phylogeny in several important details, e.g. accepting the new supraphyletic taxon Gnathifera for the Rotifera, Gnathostomulida and Chaetognatha, to which the newly established taxon Micrognathozoa (Kristensen & Funch, 2000) should now be added. Nielsen is also following recent suggestions according to which the Acanthocephala should be included within the Rotifera, despite the enormous differences in overall shape, size and life history between those gutless parasitic invertebrates and the tiny free-living animals traditionally referred to the Rotifera. Suggestions for merging acanthocephalans with rotifers have been mainly backed by molecular evidence, but Nielsen does not seem to have difficulty finding additional support from morphology. Many zoologists will be happy with Nielsen’s choice to regard the Ctenophora as the sister group of the Bilateria, that is, to move that phylum back to a much more basal position in the animal tree than was suggested in the book’s first edition. On the other hand, the author continues to defend three ideas that nowadays are less fashionable: Entoprocta and Ectoprocta as sister-groups; Phoronida and Brachiopoda as belonging to the Deuterostomata; and the defence of the Articulata, with the corresponding rejection of the Ecdysozoa concept.

Nielsen’s animal phylogeny is strongly rooted in his excellent background as a comparative morphologist. In these times of narrow specialization and one-sided enthusiasm for the molecular aspect of biology, we need to redress the balance of our phylogenetic understanding by getting insights from Nielsen’s unique knowledge of gross and ultrastructural morphology of most diverse phyla – of the less fashionable ones especially – and of their larval stages. This is not to say that Nielsen ignores or underrates the significance of modern approaches, such as numerical cladistic analyses and molecular phylogenies, two topics to which the last two chapters are devoted. His attitude towards these fashionable tools is constructively critical.

Summing up, this is not a simply a second edition of an established book. This is a really new book, and a great one at that. I am sure it will fulfil the author’s hope (Postscript, p. 523) that it ‘will be used both as an inspiration to new studies of morphology and embryology and as a source of morphological information to be integrated into molecular studies, especially of evolutionary developmental biology.’


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