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Zergling

Primary unit of the Zerg - and the most famous unit from multiplayer of SC1 - Zergling. These little creatures had returned and once again, their overwhelming number will crush the enemy. Zerglings have continued to evolve during the time leading up to StarCraft II. They can quickly transform into a glowing green creature called a “Banneling” which rolls around the battlefield and kills opponents with a suicide attack. Some people speculate, it’ll exist one more form of Zergling ensuring their usage in later phase of the game.

Mutalisk

Mutalisks are a modified form of the Mantis Screamer from the desolate Dinares Sector. It was capable of space travel even before it was absorbed into the Zerg Swarm.

For the present, the Mutalisk made an appearance only in the gameplay demonstration. In StarCraft II, its attack will still be able to strike multiple targets.

Nydus Worm

The Nydus Worm is a Zerg transport unit used to transport large numbers of small units underground. Very few details on this unit are known at this time. The Nydus Worm may be a replacement to the Nydus Canal building.