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.
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.
Many zerg ground units may burrow, become invisible and may be revealed primarily by detectors, and may not move or attack. Exceptions are the roach, which may move while burrowed, the infestor, which may move and cast Infested Terran, and the baneling, which can detonate while burrowed.
Some units can unburrow via autocast, causing them to emerge and attack when an enemy moves into range.
The ability is not smartcast.