Cave Squig

Cave Squigs are small, aggressive, generally bipedal creatures that resemble fleshy balls of muscle with legs and a maw of razor-sharp teeth, with the Cave Squig being both the most common variant and bears the most archetypal appearance that most people associate with a Squig. Many different breeds and kinds of Squig exist, but all share those same common characteristics as the common Cave Squig. Omnivores in the extreme, many Squigs live in the wild, where they feed upon either Mushrooms or whatever is unlucky enough to cross their paths.

The common Cave Squigs usually grow from around one to three feet tall and are often used extensively by Night Goblin tribes as mounts, beasts of war, or as a source of food. Like most Greenskin organisms, a Squig reproduce by means of spores released periodically by their body, which would grow underground into a plant-like womb that nourishes the Squig before it eventually emerges out of the ground. Just like an Orc, a Squig would continously grow throughout his lifetime, until they become so big that they are categorized into another larger variant called a Great Cave Squig.

Source

 * Warhammer Armies: Orcs and Goblins (8th Edition) -- pg. 62