Animus

The Animus was an alien intelligence which landed on the planet Vortis. It could take over any living creature that was in contact with gold and had already taken control of the ant-like Zarbi when the Doctor and his companions arrived on Vortis. One of Vortis' surviving lifeforms, the Optera, referred to the Animus as "'Pwodarauk'". The Animus manifested itself within an organic, self-healing palace called the Carcinome.

The Animus's true form was revealed, as resembling an octopus with some arachnid features. The Doctor, Ian, Barbara and Vicki helped the Menoptra to destroy the Animus using the Menoptra's secret weapon, the Isop-tope. After that, the travelers left the natives of Vortis to resolve their differences peacefully. (DW: The Web Planet)

Later, the Second Doctor, Jamie and Victoria returned to Vortis and encountered a seed of the Animus which had survived. The Animus was later identified by the Seventh Doctor as the Great Old One Lloigor, said to have first manifested in this universe in the Arcturus system and to have once been worshipped by the inhabitants of a lost city in Burma, which would explain its stated familiarity with Earth. (MA: Twilight of the Gods)

Eventually, the Animus perished in the Time War, and its Carcinome Walls fell into dust. (Doctor Who Annual 2006).