Zooxanthellae (plural, IPA: /ˌzoʊoʊzænˈθɛli/) are golen-brown intracellular endosymbionts of various marine animals and protozoa, especially anthozoans such as the scleractinian corals and the tropical sea anemone Aiptasia sp. They are typically dinoflagellate algae, although heterokont algae such as diatoms can also be zooxanthellae. They may be acquired by direct ingestion, and subsequently reproduce by splitting apart; a process known as budding. In other cases, zooxanthellae may be transmitted by the coral eggs and planulae. Most are autotrophs and provide the host with energy in the form of translocated reduced carbon compounds derived from photosynthesis. Zooxanthellae can provide up to 90% of a coral’s energy requirements. In return, the coral provides the zooxanthellae with protection, shelter, nutrients (mostly waste material containing nitrogen and phosphorus) and a constant supply of the carbon dioxide required for photosynthesis. Their population in the host tissue is limited by available nutrients and incident light, and by expulsion of excess cells. However, zooxanthellae do not appear to be digested by their hosts.