endosymbiotic

Of or pertaining to endosymbiosis.

The person perhaps most responsible for resurrecting and then establishing the serial endosymbiotic theory, thus creating the new field of endocytobiology, is Lynn Margulis, one of the world's foremost authorities on the evolutionary biology of the microbial world and a cofounder with Max Taylor of the Society for Evolutionary Protistology.

The endosymbiotic theory, as it came to be known, rewrote the history of life.

That lives within a body or cells of another organism. Forming an endosymbiosis.