WAEC - Biology (1995 - No. 28)

Green algae are known to form symbiotic relationships with a variety of organisms, including fungi, marine invertebrates, and some animals.Some hydra species, such as Hydra viridissima, have a symbiotic relationship with green algae. This symbiosis is characterized by the algae living within the hydra's endodermal cells, giving the hydra its characteristic green colour.