Primal hydralisk

Primal hydralisks are primal zerg creatures based off the Zerg Swarm's own hydralisk strain. According to Abathur, the primals stole the hydralisk's essence from the Swarm, and used it to produce their own hydralisks.

Game Unit
Primal hydralisks are very similar in appearance to normal hydralisks, though they are slightly larger and have greenish-gray carapaces. They also move slightly faster than their Swarm counterparts.

Heart of the Swarm
Primal hydralisks appear as enemies, and later allies on Zerus. They also appear as part of Dehaka's pack during the attack on Korhal.

Kerrigan, in her Primal Queen of Blades form, can summon sacs containing a group of primal zerg consisting of primal zerglings, primal hydralisks, and primal roaches.

Co-op Missions
Primal hydralisks can be constructed by Dehaka in Co-op Missions. They can evolve to increase movement speed and attack range, and at the requisite level, can evolve into a primal mutalisk or impaler.