Dalek-Sensorite parasite

 was a weapon which the Daleks used in the Last Great Time War. A hybrid Dalek mutant, its Sensorite DNA allowed it to exist in and affect the Interior.

Fearing that the telepathic power of the Sensorites could be turned against them, the Dalek Empire sent three Daleks to discreetly place the parasite in the Interior, succeeding despite their deaths. The parasite hid itself in a dark and loud portion of the Interior, feeding off the Sensorites' strength while increasing their fear and paranoia. When the Time Lords came to the Sense Sphere for peace talks, the parasite was detected by Susan Foreman. As the parasite drew strength from the Sensorites, Susan broadcasted the loud noise of Ian Chesterton's mobile phone through the Interior, disconnecting them all and allowing her and Ian to overpower the parasite.

Upon being presented with the parasite's corpse, the Sensorties became readily convinced of the Dalek threat and lent their aid to the Time Lords. (AUDIO: Sphere of Influence)