endosymbiont
/ˌɛndoʊˈsɪmbaɪɑnt/
noun
- An organism that lives inside the cells of another organism, usually in a mutually beneficial relationship.
- Scientists study endosymbionts to understand how complex life evolved on Earth.
- Mitochondria are believed to have started as ancient endosymbionts that lived inside larger cells.
- Some corals rely on photosynthetic endosymbionts called zooxanthellae for energy.