Deathworm Morphant

Deathworms were symbiotic creatures used by the Morgs to enable them to survive beyond death. When a deathworm was consumed, it would incubate in its host's body until the moment of death, then leave with the host's consciousness preserved inside it and seek out a new host. It could survive most assaults, including disintegration. The Master consumed one to survive his execution on Skaro. (EDA: The Eight Doctors)