Members of Balok's species were small, about the height of a Human child, and usually bald, with hair mainly on their eyebrows. Their ears were different from Humans, shaped similarly to that of Vulcans, except they were smaller and had a more flat point on top. (TOS: "The Corbomite Maneuver")
The puppet Balok
The real Balok
In a development memo of "The Corbomite Maneuver" research notes from Kellam de Forest to Gene Roddenberry on 9 May1966, de Forest twice referred to Balok's species as "Fesarian", in reference to their space craft. However, that species name wasn't included in the final draft nor the second revised final draft of the script (dated 3 May and 20 May 1966, respectively).
The Face of the Unknown establishes that "Fesarian" was just a placeholder name that the Federation used before learning their real name. They are actually called the Linnik (β), and the puppet's species is the Dassik (β), in reality a closely related species that once fought with Balok's people.