zooxanthella

[zoh-uh-zan-thel-uh]
noun, plural zo·o·xan·thel·lae [zoh-uh-zan-thel-ee] /ˌzoʊ ə zænˈθɛl i/.
  1. any of various symbiotic yellow-green or yellow–brown algae in the cytoplasm of certain radiolarians and marine invertebrates.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Word Origin and History for zooxanthellae
n.

1889, from German (Brandt, 1881), from comb. form of Greek zoion "animal" (see zoo) + xantho- (see xanthous) + Latin suffix -ella.

Online Etymology Dictionary, © 2010 Douglas Harper