StarCraft 2 Zerg Units

Zergling: The most classic unit to a Zerg Player, the Zerglings are still only .5 food to produce. They come out of the eggs in pairs and only cost one food to produce. Zerglings are the base ground "grunt" unit for zerg. The Zergling is very memorable for the capability to create a mass of zerglings at the start of the game and overrun the enemy, "zergling rushes". In StarCraft 2, the Zerglings will have the ability to become banelings, much like Hydralisks can become Lurkers. The baneling is an advanced version of the zergling, think of Headhunters -> Berserkers. The Baneling will be a very interesting unit once fully unveiled.

Zerg Hydralisk: The Hydralisk is a staple core of any Zerg Army; they are the primary Medium Assault Warrior unit. Their Core Genus (The strain they came from before the Zerg mutated them) is Slothien. For their Primary Attack, they use powerful muscle contractions to project out volleys of Needle Spines ripping apart whatever target they find, both air and ground. They have the ability to burrow into the ground allowing for deadly ambushes to occur with devastating results to any victim unlucky enough to fall into this trap.

Nydus Worm: Now we finally know what were digging all of those Nydus Canal's in StarCraft. The Nydus Worm in StarCraft 2 not only dig's these holes but has a small mouth which it can open and allow smaller zerg units to transport to. There will very possibly be a limit on how many units can pass through the small worm at once, or a cooldown timer.

Mutalisk: The Zerg's most versatile air attackers, mutalisks are known for their Glaive Wyrm that bounce-attacks several targets at once. They still look much the same as they did in StarCraft. The Mutalisks in Brood War could Upgrade to Guardian's or Devourerer's. We have no word yet on upgrades from the Mutalisk, but can expect similarities.