Sexual reproduction varies from isogamy, anisogamy to oogamy. In isogamy, gametes are non-motile as they are non-flagellated like in Spirogyra or motile and flagellated as in Ulothrix. In anisogamy, both the gametes are motile but dissimilar in size as in Eurodina. In oogamy, only male gametes are motile. These motile gametes have two unequal laterally attached flagella like in Volvox.