© 2004 Society of Systematic Biologists
Invertebrates; Invertebrate Zoology: A Functional Evolutionary Approach
Department of Biological Sciences, Auburn University Alabama USA; E-mail: ken{at}auburn.edu
Invertebrates, Second Edition.—Richard C. Brusca and Gary J. Brusca. 2003. Sinauer Associates, Inc. Sunderland, Massachusetts. XV + 936 pp. 615 illustrations. ISBN 0–87893–097–3. $109.95 (Instructor's CD available).
Invertebrate Zoology: A Functional Evolutionary Approach, Seventh Edition. Brooks/Cole Thompson Learning, Belmont, California. XVII+ 962+I-26 pp. ISBN 0–03–025982–7. $106.95 (Online resources available).
The two leading invertebrate texts, Brusca and Brusca and Ruppert, Fox, and Barnes, recently published much anticipated updated editions. For both books, the new edition offers several improvements. Trying to cover all of invertebrate biology within a single volume is a daunting task, but both texts do a good job of offering a balanced approach to the many sides of invertebrate biology. Unfortunately both also have similar shortcomings, particularly in light of recent advances in animal phylogeny and the field of evo-devo (evolution of developmental mechanisms). As expected of invertebrate texts, both books spend most of their pages marching through taxa and provide critical chapters that unify themes throughout the text.
The most obvious improvements to both texts are aesthetic. Brusca and Brusca has gone from a drab monocolored text to a book rich with color plates, organismal photos, and improved illustrations (partly due to paper quality). Ruppert, Fox, and Barnes has benefited considerably from a change in publishers from Saunders College Press to Brooks/Cole (under Thompson Learning, Inc.). With this switch, several illustrations have been improved, but color plates are lacking despite the similar price between the books. Both have added companion resources for students and/or instructors. Brusca and Brusca offers a CD filled with photos (in jpeg and Powerpoint format) that are searchable by chapter or taxonomic group. Hopefully the CD will be upgraded in the future to include many of the illustrations in the text that would be useful for teaching. In contrast, Ruppert, Fox, and Barnes took an online approach (password protected) and posted over 300 photos and 300 illustrations from their text (searchable by chapter). The downloadable jpeg files have small file sizes allowing easy file transfer, but the quality of the photos clearly suffers on high-resolution monitors. All and all, a larger investment of companion material was given to the Ruppert, Fox, and Barnes book.
Another improvement to Ruppert, Fox, and Barnes is the addition of several chapters focused on evolutionary concepts and functional morphology. In particular, the text includes information on the systematic methods and several figures of phylogenetic trees á la Brusca and Brusca, first addition. Both list relevant morphological apomorphies for nodes on the tree, which are easier to read in Brusca and Brusca, but Ruppert, Fox, and Barnes provide taxonomic labeling of interior nodes. In contrast, the layout of the second edition of Brusca and Brusca is almost identical to the first, the exception being rearrangement of five panarthropod chapters. In these chapters, considerable new material has been added and very useful text boxes have been employed for comparative purposes. Disappointingly, many other chapters were not similarly updated. For example, comparison between editions of the mollusk chapter reveals very limited revision except for the final section on evolution and phylogeny. Also in this vein, the diversity of panarthopods gets 239 well-deserved pages, but mollusks that are second in diversity only to arthropods receive 69 pages. In contrast, Ruppert, Fox, and Barnes have considerably reorganized their text to reflect a different understanding of animal relationships than in the sixth edition (which is still at odds with our current understanding—see below). They have also split up some chapters (e.g., cnidarians and ctenophores) to give a more appropriate treatment to these groups. The arthropod/mollusk balance in Ruppert, Fox, and Barnes seems more appropriate (247 pages on panarthropods in 7 chapters and 129 pages of mollusks in one chapter).
A head-to-head comparison between books of any given taxa-oriented chapter will quickly provide an idea of the slight differences in emphasis. Both provide useful synopses of taxonomic classification, phylogeny, functional morphology (e.g., feeding, gas exchange, nervous system, etc.), and reproduction. However, one noticeable difference is the emphasis of the "Bauplan" concept by Brusca and Brusca. Although this emphasis clearly has its advantages when trying to fit all invertebrate biology into a single-term course, it must be weighed against its implications about how we view animal diversity and evolution. Another difference is that Ruppert, Fox, and Barnes present a short outline at the beginning of each chapter that will be especially useful to students. Perhaps the most subtle difference, but with considerable conceptual ramifications, is the treatment of taxonomic ranks in the two texts. Brusca and Brusca present organismal groups as, for example, Phylum Annelida, Class Polychaeta, Order Phyllodocida. The same scheme in Ruppert, Fox and Barnes is presented as Annelidap, Polychaetac, Phyllodocidao. Although the superscripts still denote rank, they are much less obtrusive and I hope they are a step toward removing them in the next edition. These authors briefly discuss "downplaying the Linnean categories" in Chapter 1. Please note, however, both molecules and morphology show that "Polychaeta" is not a monophyletic clade (McHugh, 2000; Rouse and Pleijel, 2001). Clitellates, echuiran, and pogonophorans are derived polychaetes.
The texts treat higher-level phylogeny differently. Brusca and Brusca opt for the standard format of placing a single overview of metazoan phylogeny at the end of the book. In contrast, Ruppert, Fox, and Barnes, have split higher-level phylogeny up into several chunks spread throughout the text. Although this means searching for the tree of interest, it may have the beneficial aspect of keeping students more engaged in an evolutionary mindset. Specifically, it may help allow students to more thoroughly consider how all of the information they have learned for a given group bears on evolutionary history. Many invertebrate instructors have dealt with the problem of students have long forgotten what placozoans and ctenophores are by the time they get to the phylogeny chapter at the end of the book.
Although both books will no doubt be useful, they both share some major pitfalls. Foremost the treatment of recent invertebrate phylogenetic research, especially in terms of relationships between major lineages, is wanting. Since the last of editions of these books (1990—Brusca and Brusca; 1994—Ruppert and Barnes), considerable advances have been made in our understanding of animal phylogeny, many of which are incorporated into introductory biology texts. Buyer beware!—Both texts are clearly promoted by their respective publishers as including up-to-date molecular phylogenetic results. However, both texts are clearly suspicious of molecular phylogenies. Whereas the Ruppert, Fox, Barnes present both morphological and molecular trees (e.g., Bilateria, Chapter 9), they often acquiesce by stating "current evidence is insufficient to choose between these two alternative phylogenies"(p. 221). In contrast, the Brusca and Brusca text pays lip service to new hypotheses such as Ecdyozoa and Lophotrochozoa, but does not even go as far as to present a figure of these hypotheses in the final chapter on phylogeny. Results from molecular data are explained away by stating that the "field of molecular phylogenetics is still in an emergent phase" (p. 822) among other statements. (It is troubling that such a viewpoint will reach so many students.) Both texts are steadfast in their placement of lophophorates and chaetognaths as deuterstomes even though abundant data show different. The Brusca and Brusca text does not consider the Ambulacraria (hemichordates and echinoderms), which changes our understanding deuterostome evolution, and Ruppert, Fox and Barnes recognize such a clade, but appear not to have been aware of the term Ambulacraria, which has gained popularity in the last several years. This lack of consideration of molecular findings extends to treatment within groups. For example, neither considers the only rigorous phylogenetic treatment for ctenophores, Podar et al.'s (2001) molecular work. Unfortunately, invertebrate biology students may be deprived of understanding many recent molecular phylogenetic advances that have completely changed our views of animal evolution (reviewed in Adoutte et al., 2000; Halanych and Passamaneck, 2001; Giribet, 2002; Halanych, 2004—obviously these later references were not available in time for these texts, but are given for the interested reader).
The molecular data notwithstanding, both texts fail to consider the morphological data appropriately. For example, in both texts the morphology is purported to support the Articulata concept (annelids and arthropods as sister taxa) and the Lophophorata concept (brachiopods, phoronids, and bryozoans as a monophyletic clade). However, at the time these texts were written, there were several morphological cladistic analyses that clearly demonstrated morphology did not support either of these two ideas (e.g., Eernisse et al., 1992; Zrzavy et al., 1998; Giribet et al., 2000; Peterson and Eernisse, 2001). Although these objections may sound trivial, they are not. Because phylogeny is the comparative framework upon which character evolution is based, several important concepts (e.g., segmentation, coelom formation, evolution of suspension feeding) are being incorrectly presented by these texts given our current understanding of animal evolution.
Major advances made on evolution of developmental mechanisms and in paleontology were not well represented in these texts. Brusca and Brusca does occasionally mention evo-devo findings, but given how the field has changed our understanding of "Bauplan" evolution, I expected more. Curiously, Ruppert, Fox, and Barnes provide a discussion of Drosophila segmentation in the annelid chapter (p. 422), and then conclude that engrailed is expressed similarly insects and leechs. They apparently did not consider that other annelids appear to be doing something different to insects (engrailed—Seaver et al., 2001; hunchback—Werbock et al., 2001). Because comparisons of body plans is a main component of invertebrate texts and embryogenesis has historically played a pivotal role in invertebrate evolutionary hypotheses, it would have been nice to see space given to explaining the formation of body plans from a molecular developmental perspective (e.g., deployment of Hox genes and determination of body axis polarity). Additionally, fossil discoveries from Lower Cambrain Chengjiang and Sirius Passet faunas have dramatically altered our views of early animal evolution (Knoll and Carroll, 1999). As such, invertebrate texts should take advantage of this exciting new information as a way to generate student interest. Even though an invertebrate text must by necessity be limited in scope, it would be worthwhile to expose students to these exciting finds.
In a field such as invertebrate biology, where a limited number of texts serve a large community, ideas presented can take hold rapidly, and falsities can be hard to eradicate. Surprisingly, both texts included new made-up taxonomic terms, or very obscure ones, that have no formal definition or are not found in the primary literature. In such cases, I fear that the texts will ultimately introduce confusion into the literature. For example, Brusca and Brusca make up the term "Pogonophoridae" for the beard worms. However, according to the rules of nomenclature, this term is a junior synonym to Siboglinidae, a term espoused by McHugh (1997) and Rouse and Fauchald (1997), whose work both texts recognize in placing siboglinids within annelids. Brusca and Brusca also reintroduce the term "Blastocoelomates," which is basically just a reworking of psuedocoelomates or ascheliminthes. This includes groups that appear to be widely dispersed on the tree given our current understanding. The argument that a psuedocoel is not a good character is valid, but the blastocoel is clearly not a synapomorphy for the taxa in question. Similarly, Ruppert, Fox, and Barnes use terms such as Pulvinifera (i.e., Sipuncula plus Articulata) and Lophodeuterostomia (i.e., Lophophorates plus Deuterostomes). Although I certainly have been accused of interjecting complicated novel terms into the literature, it is important that they are clearly defined, not redundant, and appropriately justified based on a rigorous phylogenetic analyses.
Undoubtedly there are some issues with the new editions of both books, especially from the evolutionary prospective. Even so, all the authors should be soundly commended for accomplishing a task that many of us would loath. Both texts are still very valuable resources for the both students and researchers and will no doubt remain as the leading selling texts. As mentioned above, both also make considerable improvements over 7 previous additions due to contributions by both authors and publishers. Even though the Brusca and Brusca text appears at times to have a better grasp of the recent literature on metazoan phylogeny, the text is more skeptical and dismissive of recent findings. Ruppert, Fox, and Barnes integrated treatment of phylogeny I think is preferable and their online support will be a better teaching aid. Brusca and Brusca, however, will be appealing to students because of its superior aesthetic qualities. Having compared the two books, I prefer Ruppert, Fox, and Barnes. As a recommendation to those who may use either book, the texts will be useful for invertebrate organismal biology, but obtain a recent review of animal phylogeny as a supplement (e.g., Giribet et al., 2000; Peterson and Eernisse, 2001; Halanych, 2004).
Note: The fifth edition of Pechenik's invertebrate text (McGraw-Hill) hit shelves in Spring 2004. This text takes a more streamlined, less encyclopedic, approach to invertebrates. Although I have not seen the book yet, from talking with the author, he appears to have made a considerable effort to incorporate the latest phylogenetic hypotheses. I encourage those interested to check it out.
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Eernisse D. J., Albert J. S., Anderson F. E. Annelida and Arthropoda are not sister taxa: A phylogenetic analysis of spiralian metazoan phylogeny. Syst. Biol. (1992) 41:305–330.
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