This volume delves into the rich and diverse flora of Phycomycetes that inhabit freshwater and marine environments, excluding the well-documented groups Saprolegniaceae and Pythium. It addresses the challenges of classifying these complex organisms and incorporates discoveries in their sexuality, life histories, and nuclear phenomena. Detailed descriptions and citations of substrata, collectors, and locations accompany each species, offering a comprehensive account of these enigmatic fungi. Supported by extensive research, grants, and contributions from various scholars and institutions, this book serves as an essential resource for anyone studying or interested in the intriguing world of aquatic fungi.