Need-to-know information on the classification and identification of aquatic invertebrates This Fourth Edition of the standard reference used by generations of professionals and students is the source for authoritative information on the natural history, ecology, and taxonomy of free-living American freshwater invertebrates. Completely revised and updated, this professional field guide features a wealth of new knowledge on invertebrate animal phyla covered in the previous edition as well as fully modified sections on the preparation of materials. Other important features of Pennak’s Freshwater Invertebrates of the United States, Fourth Edition include: Current taxonomical arrangements of all freshwater invertebrate animals, excluding insects Improved graphical treatments and keys to identification, several provided by specialists Photographs and color plates to aid identification More than 300 line drawings, many new to this edition Taxonomic keys carried uniformly to genus level in all but two phyla, with frequent references to species Pennak’s Freshwater Invertebrates of the United States, Fourth Edition is an indispensable resource for biologists, ecologists, graduate students, and anyone who needs to acquire the thorough knowledge of aquatic invertebrates that is essential to understanding the community structure of freshwater environments.