Oogamy

Oogamy is a form of anisogamy (heterogamy) in which the female gamete is significantly larger than the male gamete and non-motile (egg cell). The male gametes are typically highly motile spermatozoa competing for the fertilization of the immotile egg.

Oogamy predominantly occurs in animals, but can also be found in many protists, certain orders of algae (Ochrophytes, Charophyceans), and some plants such as bryophytes, ferns, and some gymnosperms like cycads and ginkgo.

In some algae and most gymnosperms and all angiosperms, a variation of oogamy occurs where the sperm cells are non-motile as well.