The Lactrans were a civilization native to the planet Lactra VII. The Lactrans resembled 30 meter-long slugs, but were regarded as being highly intelligent, as well as possessing telepathic abilities which were beyond Vulcan abilities.
In 2270, the USS Enterprise visited the planet on a mission to investigate the disappearence of the USS Ariel. Captain James T. Kirk and his crew soon discovered that the Lactrans had placed the Ariel crew into a type of zoo which housed different types of animals. (TAS episode & Star Trek Logs novelization: The Eye of the Beholder)
While compiling a report of the planet Orisha and its native inhabitants in 2380, Commander Deanna Troi identified the dominant inhabitants as being a insectoid species similar to the Lactrans, the Xindi, and the Nasat. (TTN novel: Sword of Damocles)