Primal ultralisk encompass a variety of primal zerg strains, and exhibit a high amount of variety in their appearance, with some closely resembling the ultralisks of the Zerg Swarm and others being better suited to life on Zerus.
Primal ultralisks are drastically different from their Zerg Swarm counterparts, being significantly smaller, possessing lower health, and lacking the large shield-like carapace above a normal ultralisk's head. They also attack differently, as their kaiser blades, instead of being mounted to their backs, are attached to their front legs in the form of large, retractable claws. They also look more similar to ravasaurs, Brakk and tyrannozor.
Primal ultralisks are encountered throughout the campaign of Heart of the Swarm as both enemies and allies.
The primal ultralisk originally had a "Devour" ability, where it swallowed a non-massive enemy unit. The enemy unit would not be destroyed, but would be removed from battle and take damage over time as long as it remained swallowed. Destroying the primal ultralisk frees the swallowed unit.