The stramenopiles are a major group of eukaryotes, including the heterokonts and a few close relatives. These are distinguished by having tripartite mastigonemes, or are secondarily derived from forms that do. In addition to the heterokont algae, they include the following:
- Water molds, Hypochytrids - groups superficially similar to fungi
- Bicosoecids - a small group of heterokont flagellates
- Labyrinthulids, Thraustochytrids - small groups similar to slime molds
- Proteromonads, Opalines - small groups of flagellates