Deneva Mind Parasite
A parasitic organisms that consisted of a swarm of large pancake-like organisms. The monster was featured in the TOS episode: Operation Anniliate!
The parasite is noted for it's large number of small pancake shaped structures. In function each section of the parasites acts like a large brain cell and it attacks it's victims by making use of it's limited flight to latch onto the spinal column of the intended victim. The beings have a unknown means that allows all of the organisms to act as a single large entity.
Nature of their parasitic functions
The creatures are not capable of manipulating objects outside of their own forms but using the tendrils that they inject into the nervous systems of their victims they are able to make use of the higher functions of the infected beings in order to facilitate the infection and spread of the species from planet to planet. Due to their means of controlling the infected victims, the pain caused by the parasites leads to eventual madness and death of the victims.
Because of the mental disciplines of the minds and training of Vulcans, they are able to limit and resist the control of the parasites.
How the creature reproduces was not determined as Kirk decided that ending the infection was more important then it's basic biology. However once they had been brought to Deneva they did spread until they had infected the entire population of the colony.
Cure and Destruction
Due to the destructive and deadly nature of the parasites, Captain Kirk determined that the creatures must be destroyed. During the initial investigation on the Planet of Deneva Mr. Spock was attacked and infected with one of the parasites. Also finding a cure to the infection had a personal connection with the commander of the Enterprise as among the infected victims was Kirk's brother, sister-in-law and nephew. Unfortunately, Kirks brother, George, was found dead when Kirk arrived at the scene and his sister-in-law died while under treatment on board the Enterprise.
After being infected by the creatures, Spock initially was lead by the infected parasites to try and take over the ship trying to send it out of the system. Once Spock had used his Vulcan mental discipline to control the manipulations of the creatures, he was allowed to return to the surface to collect a specimen for study.
Using information that was hinted at when a suicidal Denevan, trying to prevent the spread by flying his single man ship into the Denevan sun, was freed just before his ship fell into the sun. Kirk, Spock and Dr. McCoy were able to determined that the at a certain intensity light would destroy the creatures. The theory was tested on the specimen killing it. When testing to see if the same treatment would free an infected victim, Mr Spock was volunteeringly placed in the test chamber and the infection was destroyed. The unfortunate side effect was Spock being blinded. Much to Dr. McCoy's regret it was later determined that only Ultra-Violot light would have been actually required making that blindness unnecessary.
To destroy the parasites, Kirk deployed Ultra-Violet generating satellites and they were used to exterminate the creature. Unlike with the case of the Silicon Entity, no one seemed to care that they were making an entire species extinct.