is a complete, trusted, and engaging textbook whose comprehensive coverage makes it an invaluable resource for both undergraduate and graduate courses and professional researchers. The third edition has been widely praised for its detailed classifications, high-quality illustrations, and coverage of contemporary debates in the field. The fourth edition continues to feature recent scholarship and current perspectives while streamlining the text to improve accessibility for intro-level students. Gonzalo Giribet joins as coauthor, contributing his phylogenomic expertise as an Evolutionary Biologist and Phylogeneticist and Director of Harvard's Museum of Comparative Zoology.