symbiont
Symbiosis (from Greek συμβίωσις, symbíōsis, "living together", from σύν, sýn, "together", and βίωσις, bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasitic.
The organisms, each termed a symbiont, must be of different species
https://en.wikipedia.org/wiki/Symbiosis