Invertebrates, Second Edition presents a modern survey of the 34 animal phyla (plus the Protista) and serves as both a college course text and a reference on invertebrate biology. Thorough and up-to-date, it is organized around the themes of bauplans (body plans) and evolution (phylogenetics). Each phylum is organized in a standardized fashion, treating the systematics, bauplan (support and movement, feeding and digestion, circulation and gas exchange, excretion and osmoregulation, nervous system, reproduction and development), and phylogeny. Detailed classifications, phylogenetic trees, and references for all phyla are provided. Tables summarize each phylum's defining attributes. The text is accompanied by an abundance of detailed line drawings and—new to this edition—color photographs.

Other key changes from the First Edition (1990) include:

* the incorporation of new developments in phylogenetics, developmental biology, and molecular genetics
* major changes at the highest levels among the invertebrates. Three phyla that appeared in the original book—Pentastomida, Pogonophora, and Vestimentifera—no longer exist, and a new phylum, Cycliophora, has been erected. Moreover, this edition discusses recent work in molecular systematics that has shaken classic views on animal classification.
* a large new section on "Kingdom Protista" (replacing "Protozoa") containing new contemporary views of these organisms (arranged in 18 phyla).