From an unknown planet, the Animus 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.
At the end of the story, the Animus's true form was revealed, as resembling an octopus with some arachnid features. The First Doctor, Ian, Barbara and Vicki help the Menoptra to destroy the Animus using the Menoptra's secret weapon, the Isop-tope.
The Animus has returned or been mentioned in several spin-off stories. In the Missing Adventure Twilight of the Gods by Christopher Bulis, the Second Doctor, Jamie and Victoria return to Vortis and encounter a seed of the Animus which had survived. The New Adventure All-Consuming Fire by Andy Lane identified the Animus with Lloigor, one of the Great Old Ones from H. P. Lovecraft's Cthulhu Mythos. An article by Russell T Davies in the Doctor Who Annual 2006 says that the "Greater Animus perished" in the Time War, "and its Carsenome (sic) Walls fell into dust."