Symbiont
A Trill symbiont, or simply, a Symbiont, is a sentient parasitic, larvae-like lifeform from the planet Trill. They live primarily in a symbiotically nature inside their Trill hosts. Due to having multiple hosts, many symbionts gained distinguished reputations. Compared to most humanoid species, the Symbionts could easily live many hundred of lives by way of Trill hosts.
Physiology
"Teardrop" in shape, Symbionts can swim in their natural pools. The symbionts communicated with each other via electrical impulses, transmitted through the milky water that they inhabited. They also had a limited form of communication with certain Trill while not joined. The Symbionts and the Trill do not necessarily need each other to survive, but it is a great honor to be chosen to be the Host of a Symbiont. The two are joined through a surgical procedure, in which the Symbiont is placed in the Trill's abdomen. Once the two are joined, both the Host Trill and the Symbiont do become dependent on each other. The trauma caused by the removal of the Symbiont would cause the Trill to go into shock, and the Symbiont by itself would be too fragile to survive on its own.
Sometimes, symbionts were born with a rare biochemistry that made them unfit for joining. This occurred only once every hundred years or so.
A Symbiont never loses the memories of the past lives it has lived, though they may fade.
A Trill that has joined to a Symbiont will gain these memories, and remember the emotions the Host at the time felt while the events were happening.
Society
The "Symbiosis Commission" oversaw the joining of Symbionts and humanoid Trills, and through this Commission, the Symbionts were cared for by "Guardians."
Symbionts are implanted only into Trill that had undergone a rigorous testing process put forth by the Commission.
In the 24th century, 500 symbionts became available for joining each year, compared to the 5,000 humanoid Trill who annually apply to become Hosts.
In order to hide the political implications of these numbers, the Trill government led the public to believe that only one in every 1,000 Trills was suitable for joining.
This was also done out of concern and fear for the Symbionts, as the scientific and political community felt that the Symbionts could come to be viewed as mere prizes or commodities to be fought over.
Until the mid-24th century, it was not made public to other species that that Trill were actually a joined species, as the people considered an extremely private matter.
Once the people of Trill branched out, new hosts for a Symbiont often had to create cover stories as to why they knew certain information.
