"Threshold" will live on in infamy for Star Trek fans because many know it as the episode in which Tom Paris and Janeway ...

Explaining the different kinds of photonic lifeforms in the "Star Trek" universe and how these beings function.

But fans will remember one particular symbiont the most, Dax, thanks to its incorporation with the most famous Trill host, Jadzia (played by Terry Farrell), from Star Trek: Deep Space Nine.