Pennak’s Freshwater Invertebrates of the United States, 4th ed.

Pennak’s Freshwater Invertebrates of the United States, 4th ed.

Hairston, Nelson G Jr

Pennak’s Freshwater Invertebrates of the United States, 4th ed. DOUGLAS GRANT SMITH. John Wiley & Sons, New York, New York, 2001, 638 pp., $120 (ISBN0-471-35837-1).

“Pennak” is one of those reference books that everyone in the field simply refers to by the author’s last name-a sure sign that it has become a standard. In my own lab, I have all of the first three editions of Pennak on the bookshelf, and the binding is falling apart on each of them from repeated use. Now comes a fourth edition, but this time Robert Pennak himself did not undertake the task of reworking his classic. Rather, Douglas Grant Smith has made extensive revisions to the book while still retaining its major features, and while folding the founding author’s name into the title. The subtitle of the book “Porifera to Crustacea” identifies the book’s new, more restricted taxonomic range. The third edition of Pennak dropped coverage of insects, and Smith’s new edition also drops the protists. This new edition, however, remains faithful to the tenor of Pennak’s original vision: each phylum included is described in the style of a textbook on invertebrate zoology with sections covering anatomy, physiology, reproduction, ecology, and geographic distribution. Following this are sections on collecting, preservation, and taxonomy after which comes a key to the organisms, all of which push the book in the direction of being a taxonomic guide.

It has always seemed to me that this structure embodies both the strengths and the weaknesses of Pennak’s book. The strengths are that any novice student can gain valuable insight into the fundamental features of an organism she or he has just collected, and can make some headway in working out its identity. The weaknesses are that the discussions of basic zoology cannot go into the kind of detail found in a genuine invertebrate textbook, and the keys are necessarily incomplete giving only partial coverage of many groups. Indeed in this new edition, the effort undertaken in previous editions to provide keys to species for the major phyla has been completely dropped and replaced by keys to genera. As a result, many professional scienlists will likely be dissatisfied with the lack of specificity provided.

So, for whom is the book intended? At $120 a pop, it is unlikely to be adopted as a course textbook, while as a reference work is it not entirely satisfactory. And, if this is the case, why are the copies of previous editions in my lab so well worn? I think the answer lies in what Smith calls in his preface to this edition “the enormous breadth of aquatic invertebrate diversity and biology.” Few people, myself included, are expert in more than a few of the groups found in freshwater, yet we often encounter strange and wonderful organisms as we go about collecting the specimens in which we are particularly interested. Pennak provides our first guide to what these animals might be and how they make a living.

For the most part, Smith has produced an attractive, updated version of Pennak that readers of earlier editions will still recognize. While adding a number of excellent new illustrations, especially SEMs (De Smet’s micrographs of rotifer trophi are astounding!), people who have thumbed earlier editions will encounter many old friends: for me these include a fuzzy micrograph of a Daphnia ephippium that has somehow made it into all four editions, and Fryer’s beautiful illustrations of cladoceran anatomy that first appeared in the second edition. Naturally, I have looked most closely at the groups I know best, and although I find them generally excellent, I did encounter a few mistakes and several disappointments. In the chapter on the Cladocera, Smith does not address the much-discussed question of whether this Order really is a valid monophyletic group. In addition, although in a useful new section of the introduction on exotics to North American waters both Bythotrephes and Cercopagis are listed, the latter does not appear in the taxonomic key. and the figure of the former has as its legend “Bythotrephes (or Cercopagis) . . . ” as if they were either the same thing, or the author was not sure which was illustrated. In the chapter on the Copepoda, Smith writes, as Pennak did before him that he reluctantly accepts the elevation of what were previously subgenera in the genus Diaptomus to generic status, but in his new genus-level-only key, Smith repools all but one of them into a single large genus (Diaptomus). It would have been more appropriate simply to stop the key at the family Diaptomidae and not include the inconsistency. Besides, the other diaptomid genus included, Acanthodiaptomus, Smith misnames “Actinodiaptomus” in two places.

One other concern becomes apparent on reading much of the text. Whereas the new sections have reasonably up-to-date literature citations, the older sections are often little revised, and the references used are badly out of date. For example in three pages covering cladoceran reproduction, male production, resting eggs, development and life cycle, there are only three literature citations given and two of these are to papers published in 1929 and 1939 (the third is 1985). Likewise in four pages on copepod reproduction, metamorphosis, parasitic copepods and ecology, the four references cited are from 1933, 1940, 1942 and 1988. As excellent as these older studies are, they are not particularly useful for students looking for guidance to the current literature.

Despite these shortcomings, the book remains a practical introductory reference to the broad diversity of freshwater invertebrates (minus protists and insects). I will put it on my reference shelf where I am sure it will, like its predecessors, become worn with use.


Department of Ecology and Evolutionary Biology

Cornell University

Ithaca, New York 14853


Copyright Society for Integrative and Comparative Biology Dec 2001

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