• Roaches: new low-power, fast moving starting unit.
• Infestors: take the place of the original game's Defilers, using the same Dark Swarm special ability as well as new Disease and Infestation abilities.
• Corruptor: new anti-air unit that doesn't actually attack flying baddies, but "corrupts" them, forcing them to fight each other.
• Swarm Guardian: upgraded Guardian, maintaining its strength against ground units while gaining the ability to hatch Broodlings.
• "Toxic Creep": created possibly via Zerg Queens

So far, those are just the new information gathered for the Zerg Swarm. To know how these units feel like, watch the video clip below. Enjoy!

Via 1UP