Swamp monster

The Swamp Monsters were a race of monsters that live in thick, muddy swamps. They have small brains and so are not very clever. They use cords to attach to other beings and use their intelligence to survive. They reproduce by exploding and the pieces each become new swamp monsters. It affected the otters. The Doctor and Martha Jones came across one on the planet Sunday. It tried to use a nuclear explosion to multiply itself. The Doctor prevented the explosion and tricked it into using his TARDIS to multiply. It then attached itself to the Doctor, who defeated it. (NSA: Wetworld)