Lake Monster

The Lake Monster was a tentacled creature, a biproduct of the Thousand Year War on Skaro. It lay deep in the Lake of Mutations. Ian Chesterton compared it to a jellyfish and found its cells extremely mutated. The First Doctor theorised it must have started as a small mollusk but in time turned into a monster. It had low intelligence and could blend in to its surroundings. This made it hard for even Daleks to detect it. (TV: The Daleks)