Antoim

The Antoene were aliens described by Vicki Pallister as "great round things covered in spikes that float and smother and kill." The Fifth Doctor noted that they were remarkably stupid.

Vicki and Steven Taylor were being chased by them when they met the "Locum" Fifth Doctor in the TARDIS before a trip to Ravenna in the year 540.

The Antoene turned out to be an intelligent virus who passed through a dimensional instability making them expand thousands of times larger than they should be. The Doctor was able to, using parts from the Monk's TARDIS, create a device that shrank them back to their normal size. The Ostadi then released an antibody that dealt with them. (AUDIO: The Secret History)