Lactran

From Memory Alpha, the free Star Trek reference

The Lactrans are a civilization of 30-meter-long slug-like lifeforms inhabiting the planet Lactra VII. Despite their appearances, they are highly intelligent and telepathic beyond Vulcan abilities.

They keep a zoo of animals on their planet, and keep intruders away by altering their sensor readings to mask their life-signs.

In 2269, the crew of the USS Enterprise visited Lactra VII on a mission to investigate the disappearance of a scientific team from the Ariel. (TAS: "The Eye of the Beholder")