A uniped was a type of small animal.

In 2269, during the battle between Spock and Spock One on Organia, Captain James T. Kirk (due to the effects of the thought-shield) saw the drowned bodies of a wide variety of small animals, including unipeds. (TOS novel: Spock Must Die!)

Unipeds are presumably creatures with one foot, and have appeared several times in fiction and mythology.