Nydus worm

The Nydus Worm is a StarCraft II Zerg transport unit.

StarCraft: Ghost
The Nydus Worm, or some variant, may have originated in StarCraft: Ghost. Although there are key differences in the two portrayals, namely that the Nydus Worm in StarCraft II is far more solid, the concept may have originated earlier.

StarCraft II
The Nydus Worm can be used to transport as many units are selectable (up to 255 in the current build). It cannot transport Zerg defensive structures.

The units are transported to a fixed location.

The Nydus Worm works like a Ghost nuke; the player places a beacon, and a few seconds later the Nydus Worm pops up.

The Nydus Worm is visible while transporting units underground and is capable of traversing gaps between space platforms. When emerging from the ground, it sticks out vertically.