: Symbiodinium sp
Zooxanthellae are a very special type of marine plant . They are single celled algae which live inside the translucent fleshy tissue of many marine animals including types of giant clams, nudibranchs and even jellyfish, however they play their most important role when living within coral polyps. Like all other plants zooxanthellae need sunlight in order to photosynthesise and grow.
Photosynthesis produces sugars essential for the plants to grow, however with the zooxanthellae enough sugar is produced to allow some to be shared with their hosts. In return the host will assist the growth of the zooxanthellae by passing on some of its dissolved organic waste. The host animal cannot usually survive if the zooxanthellae are not present. There are several different species of zooxanthellae, typically grouped together as the genus Symbiodinium
The host animals do not have any zooxanthellae in their larval forms and therefore must acquire them from the water column. The juvenile host filters the zooxanthellae from the seawater along with its food and once in the stomach of the host the zooxanthellae is passed into the surface flesh. Zooxanthellae multiply within the host by simple cell division.