Invertebrate Zoology deals with the animals that have no backbones, including the shrimps, crabs, sponges, worms, snails and squids. This book deals specifically with the invertebrates that spend all or part of their lifecycle in a freshwater environment. (As is usual and as in the previous edition, aquatic insects are excluded due to their vast numbers.) The invertebrate species far outnumber the vertebrate species, and a through understanding of aquatic invertebrate zoology is essential to understanding the community structure of freshwater environments.