Evolutionary Dissent

For anyone who has ever considered the bizarre panoply that composes the Echinodermata, it is difficult to lose sight of the fact that echinoderms are strange. Their ontoge­ netic twists and turns of symmetry, absence of certain familiar organ systems, and pres­ ence of some less familiar systems might tempt one to imagine an extraterrestrial origin for the Echinodermata. In spite of this, echino­ derm specialists have not been deterred in their search for more conventional origins of this strange phylum. Conventional, perhaps, but not prosaic. We have come a long way since Bather made the statement quoted above. Previous works, such as Cuenot (1948), Nich­ ols (1969), and Jefferies (1986), have provided single "snapshots" of the sometimes icono­ clastic views held by their authors. However, no other books give the comprehensively pluralistic overview of the question of echi­ noderm origins and class relationships that Echinoderm Phylogeny and Evolutionary Biology attempts to provide. This compendium of 26 papers presented at a December 1986 London symposium (that bore the same name as the book) is needed now more than ever. We need to step back and see in which directions a phylogenetic approach will take us with this perplexing group of animals. Because over half the papers in Paul and Smith's book use cladistic methods to present their arguments, I will rely on a similarly cladistic viewpoint to evaluate the strengths and weaknesses of this new tome. Although the phylogenetic papers present discordant results, it is not the actual use of cladistics that produces the dissension. Detractors of cladistics cannot deny that the method forces authors to lay all their cards on the table. For this reason, the most interesting undercur­ rent in Paul and Smith's book is that it is character analysis that leads to discord, not the method itself. I would like to follow this un­ dercurrent a little, to illustrate the value of Paul and Smith's book. The uniqueness of the echinoderms (Nich­ ols 1975) and the unusual features of echi­ noderm classes have spawned many disparate notions of their origins and homologies. If disparity of opinion is a sign of health, then echinoderm evolution is a vigorous and vital discipline indeed. Echinoderm Phylogeny and Evolutionary Biology is a testament to this vi­ tality. The "dissent" of this review's title is not acrimonious. Rather, it is a carefully de­ fended set of opposing views that are mu­ tually illuminating. Throughout the book, we are repeatedly presented with differing in­ terpretations of the homologies of characters deemed important in unraveling not only the origins of the phylum, but relationships among the classes. These interpretations ne­ cessitate reexamination, if not of the basic ar­ guments, then at least of the essential features of the organisms themselves. With each new approach to the problem of homology, our understanding of the biology of the clades involved is enriched. It is also interesting to note how often it becomes necessary to reex­ amine even the basic morphology of larvae and adults in order to bolster arguments for one phylogeny or another. All this "descrip­ tive" biology is flourishing in an age in which systematics and whole animal studies are often regarded as passe. The papers in this book testify against the latter myopic view and jus­ tify a healthy interest in research that asks: what is this beast, what does it do, and to what is it related? As Bather (1900) noted, their strangeness makes it difficult to relate echinoderms to ottjr er major animal groups. Interpjhylum relaReview