Includes bibliographical references and index.

Introduction and Environmental Considerations -- Invertebrate Classification and Relationships -- The Protists -- The Poriferans and Placozoans -- Introduction to the Hydrostatic Skeleton -- The Cnidarians -- The Ctenophores -- The Platyhelminthes -- The Mesozoans: Possible Flatworm Relatives -- The Gnathifera: Rotifers, Acanthocephalans, and Two Smaller Groups -- The Nemertines -- The Molluscs -- The Annelids -- The Arthropods -- Two Phyla of Likely Arthropod Relatives: Tardigrades and Onychophorans -- The Nematodes -- Four Phyla of Likely Nematode Relatives: Nematomorpha, Priapulida, Kinorhyncha, and Loricifera -- Three Phyla of Uncertain Affiliation: Gastrotricha, Chaetognatha, and Cyliophora -- The 'Lophophorates' (Phoronids, Brachiopods, Bryozoans) and Entoprocts -- The Echinoderms -- The Hemichordates -- The Xenoturbellids: Deuterostomes at Last? -- The Nonvertebrate Chordates -- Invertebrate Reproduction and Development: An Overview.

Covers the phyla of invertebrates (comprehensive) with an emphasis on unifying characteristics of each group.