ZOOXANTHELLA

any flagellate protozoan, sometimes classified as a yellow-green alga, with yellow or brown pigments contained in chromatophores. Zooxanthellae live in other protozoa (foraminiferans and radiolarians) and in some invertebrates. They use the carbon dioxide and waste materials of the host, supplying, in return, oxygen and food substances. Zooxanthellae spend their resting stage in the host; at times they escape and become free-swimming, independent flagellates. Examples of zooxanthellae are Cryptomonas (see cryptomonad) and Chrysidella.