Need-to-know information on the classification and identificationof aquatic invertebrates This Fourth Edition of the standard reference used by generationsof professionals and students is the source for authoritativeinformation on the natural history, ecology, and taxonomy offree-living American freshwater invertebrates. Completely revisedand updated, this professional field guide features a wealth of newknowledge on invertebrate animal phyla covered in the previousedition as well as fully modified sections on the preparation ofmaterials. Other important features of Pennak's Freshwater Invertebrates ofthe United States, Fourth Edition include: * Current taxonomical arrangements of all freshwater invertebrateanimals, excluding insects * Improved graphical treatments and keys to identification, severalprovided 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 twophyla, with frequent references to species Pennak's Freshwater Invertebrates of the United States, FourthEdition is an indispensable resource for biologists, ecologists,graduate students, and anyone who needs to acquire the thoroughknowledge of aquatic invertebrates that is essential tounderstanding the community structure of freshwater environments.