Internal siliceous element with three branches. Flagella hard to see. Sometimes with multiple nuclei. Widespread in coastal temporate, tropical and boreal waters, less common in oceanic areas; eurythermal and apparently somewhat euryhaline. Possibly only one species. : E. tripartita (Shumann, 1867) Lemmermann 1899. Nutrition herbivorous, primarily nanoplanktonic diatoms, occasionally dinoflagellates.