Symbiont-free individuals of the sea anemone Exaiptasia pallida, an established model system for the study of cnidarian-dinoflagellate symbiosis, were colonized with the "normal" (homologous) symbiont Symbiodinium minutum (clade B1) and the heterologous Symbiodinium trenchii (D1a). Transcriptomic profiles of homologous, heterologous and aposymbiotic (bleached) symbiotic states were compared and host gene expression profiles were evaluated to determine molecular processes underlining host-symbiont compatibility.