Swamp monster

The Swamp Monsters are a race of aliens that live in thick, muddy swamps.

Anatomy
Each swamp monster consists of a large, gelatinous mass that houses the brain and other vital organs. They also have a number of large tentacles protruding from the central mass. The brain and nervous system are spread across the body, meaning that their ability to think is slow. They keep their bodies submerged in water because they are so large and interact with dry land using their tentacles. Each tentacle can penetrate the skull of another being; this allows it to control them in a similar fashion to a puppet. By attaching tentacles to other beings, a swamp monster is capable of utilising their skills and intelligence.

Their lack of intelligence means that they act mostly on instinct to survive. As mentioned, they can use other species to help achieve their goals. For example, the Swamp Monster on Sunday utilised humans to communicate with others. It also used a protein-RNA mix to control smaller animals, such as the Sundayan Otters; this mix implanted memories and images into them and generally led to a rise in aggression.

They believe that reproduction is the purpose of life; they achieve this by blowing their bodies up. A powerful enough explosion can project each piece of swamp monster into space, where they can spread to other planets, in a similar fashion to Stage Trees, Krynoids or the Comet Flowers on Besseme.

Invasion of Sunday
A small piece of another swamp monster landed on the planet Sunday inside a meteorite that struck the planet. It took time to establish itself; the colonists first noticed that something was different when the local otters became more aggressive. After the arrival of The Doctor and Martha Jones, the creature began to attack the colony. It killed and took control of Pallister the head of the Sundayan Council and former nuclear technician, intending to use his knowledge of nuclear technology to build a nuclear weapon and blast itself into space and spread to new worlds. The Doctor managed to defeat it by allowing it to begin to take control of him; he then injected the creature with a new protein-RNA mix, designed to destroy its outer membrane. The creature died shortly after. (NSA: Wetworld).