At this time little official information has been released by Blizzard about the Zerg units, so this list has been compiled by viewing gameplay footage and leaked sources.

Zergling

The zergling returns in StarCraft 2 as the swarming Zerg base unit (similar to the Terran marine or the Protoss zealot) capable of amassing in terrific numbers to overwhelm their opponents.

It appears that the zergling in StarCraft 2 will be very similar if not exactly the same as the zergling from the original StarCraft and Brood War. A weak but fast unit, the zergling is at its maximum damage in a large group attacking from various sides. A head-on zergling assault against an equal enemy usually results in a mass of blood and little damage to the opponent.

Mutalisk

The most versatile flying unit in StarCraft - the Mutalisk - makes its appearance in SC2 playing what seems to be the same role. Mutalisks are relatively affordable air units with comparatively lower damage and lower health than fliers of other races. They, like many other Zerg units, have the ability to swarm or to be produced early and in good numbers to really wreak some havoc!

Mutalisks also seem to have retained their multi-hit spore attack which would do full damage to the main target and then partial damage to 2-3 other nearby targets.

Baneling

The first new unit announced for the Zerg in StarCraft 2, the baneling is an evolution of the zergling and seems to take the place of the Infested Terran, which lets be honest was never really a serious part of StarCraft. Much like the infested terran, the baneling is meant for suicide bombing. The main difference here is that the baneling can morph from zergling - a unit that every Zerg player will have an abundance of anyway. Therefore the baneling should play a strategic role in SC2 that the infested terran never saw. Time will tell.

Nydus Worm

Borrowing its name from the Nydus Canal (a structure in the original StarCraft), the Nydus Worm serves a similar purpose. It transports zerg units across long tracks of land very quickly. It is not yet known what tier this unit is or how well it will perform strategy-wise in StarCraft 2. The Nydus Canal was a solid unit but was only used sparingly and in very few late game situations. The fact that the Nydus Worm is mobile may make it more likely to appear in multiplayer than the Nydus Canal.