The Oomycetes are the largest group of heterotrophic Stramenopiles. They are found all over the world in fresh and salt water habitats. Some of the terrestrial Oomycetes are among the most important plant pathogenic organisms that may be facultatively or obligately parasitic. The organisms range from those preferring well-aerated streams to some that occur in stagnant waters and that may gain most of their energy from anaerobic metabolism. Most members of the group are filamentous and lack septa except where reproductive cells are produced, but holocarpic forms are found in the Saprolegniales and Lagenidiales. The cell walls of the group consist mostly of ß-1,3- and ß-1,6-glucans with a small amount of cellulose. A few members also have chitin deposits.
All members of the group that have had extensive life cycle studies have been found to be diploid in the vegetative phase with meiosis occurring during gametogenesis. The group is characterized by oogamous reproduction that includes interaction of male antheridia with female oogonia.
You may wish to look at a Berkeley site that discusses the Oomycetes.