Rockworms

Rock Worms are the most dangerous enemies ancountered in the underground of Mars. Not only have they grown to huge size, they are also very fast, heavily armoured and can kill a lesser man with one bite. Even worse, their skin is coated with acid!

Their size is propably because of their habit of living near Radium. Too bad that often the adventurer needs exactly this mineral to advance further.

Lore
''These gigantic tube worms live coiled up under the earth with only a hard, slime-covered tube visible at the surface. The tubes are made of a caustic material regurgitated by the worm. This same acidic ooze coats and lubricates the rockworm's body, allowing it to emerge with startling speed from its subterranean resting place. The slightest vibration on the surface draws the rockworm out. The speed of its attack, the caustic ooze and a horrible thorny maw make each rockworm a threat. Making matters worse, rockworms tend to clump together in colonies and can be vicious when provoked. They are best left undisturbed whenever possible.''

- from "Mysteries of the Red Planet", Martian Dreams