Some species of cocciod green algae live as symbionts (zoochlorellae) in the cells of many single-celled species from groups such as the amoebae, the ciliates or the foraminifera. However, zoochlorellae are also known in animals such as freshwater polyps, other groups of coelenterates, in freshwater sponges, turbellarians, etc. These symbioses are generally mutually beneficial, the hosts benefit from secreted assimilates of the algae, and the algae are better protected from grazing due to the size of the hosts.

When the hosts lack food, part of the zoochlorellae is usually digested.

Sample from a freshwater aquarium.