zooxanthella

noun2

1. •
   Any of various typically yellow-brown dinoflagellates (originally grouped as genus Zooxanthella) now assigned to the genera Symbiodinium and Amphidinium, notably found in coral reefs.

   • The zooxanthellae produce carbohydrates, via photosynthesis, and the polyps harvest these carbohydrates, much as farmers harvest corn. — 2014
2. •
   (no longer used) Any of the yellow pigmentary particles, or minute corpuscles of yellow coloring matter, found in certain radiolarians.