M-113

M-113 is a desolate planet that was once home to an ancient and long dead civilization, as well as the homeworld of an indigenous species known as the M-113 creature or "salt vampire".

In 2261 archaeologist Robert Crater and his wife Nancy began an expedition on M-113 to conduct a survey of the planets many ruins. Unknown at the time of the Crater expedition, a single surviving member of the "salt vampire" race continued to live on the planet. It would eventually kill Nancy and would continue to live along with Robert until 2266. (TOS: "The Man Trap")

It is known that the salt vampire are intelligent but it is unclear whether the ruins belong to them, or another sentient species on the planet.