The Slithergee were a race of obsequious alienslugs whose home planet was destroyed.
Slithergees were blind creatures and hunted their prey by scent. Slithergees also used slaves as sight guides and had a fear of darkness.
A spacecraft carrying the Slithergee arrived in the orbit of the colony planet Puxatornee, requesting the permission to settle on the first moon. Otherwise, they would humbly threaten to declare all-out war. Interference from alternate futures — unwillingly aided by the Seventh Doctor — resulted in the creation of two timelines branching out from this event, with one timeline seeing a war being waged between the Slithergee and the human colonists that reduced Puxatornee to a radioactive cinder and the other seeing a policy of appeasement towards the Slithergee going so far that the Slithergee took complete control of the colony and prosecuted human objections as "hate crimes". (AUDIO: Flip-Flop)
River Song thought she recognised Slithergee architecture in the buildings generated by the ruins of a prototype TARDIS. (AUDIO: Lies in Ruins)
Behind the scenes
The Slithergee also appeared in the first instalment of a Big Finish Productions audio series featuring Vienna Salvatori as the titular character. This series is not currently considered part of the DWU.