zo·o·xan·thel·la 
(zō′ə-zăn-thĕlə)
(zō′ə-zăn-thĕlə)n. pl. zo·o·xan·thel·lae (-thĕlē)
Any of various yellow-brown photosynthetic dinoflagellates that live symbiotically within the cells of other organisms, especially certain corals and other marine invertebrates.
[New Latin : ZOO- + XANTH(O)- + -ella, diminutive suff.]