Circassian Cat

Circassian Cats are a non-sapient species of funny-looking creatures that can be kept as pets by Humans in the 24th century.

On the other hand, "Circassian Plague Cats" are known for their hostility. It's not known whether these are a different species, subspecies, or regular Circassian Cats affected by some kind of disease like rabies.

Biology
Like Tribbles, Circassian Cats have spherical bodies entirely covered in fur, and likewise come in several color patterns. Their fur has adhesive properties, allowing them to cling to most surfaces. While limbless, they have a pair of sensory appendages that wag when they're excited. They gain sustenance from emotions and, when left alone, are prone to wandering around looking for "food", which often leads them to trouble.

Appearances

 * Star Trek: The Next Generation, s04e16, "Galaxy's Child" (1991)
 * Star Trek: The Next Generation, s05e12, "Violations" (1992)