Unicellular, symbiotic algae living within coral polyps that produce food for their hosts by
photosynthesis; Tiny plants that live in a symbiotic relationship with certain corals, clams, and some sponges; Symbiotic dinoflagellates in the genus Symbiodinium that live in the tissues of a number of marine invertebrates and protists; A generic term for small, autotrophic
bacteria or protists which are found as endosymbionts of metazoans (nudibranchs, corals, etc.) and radiolarians.