Tersuron

The Fendahl Predator consumed the Tersurans' and the Delphons' best forms of communication, so they had to evolve for the most tenuous forms of communication. (PROSE: The Taking of Planet 5)

Invalid Appearances
The Tersurons were a species that lived on the planet Tersurus. (NOTVALID: The Curse of Fatal Death)

Culture
Tersurons were the nicest race in the universe, but also the most shunned and loathed as they spoke Tersuran, a language of controlled farts. (NOTVALID: The Curse of Fatal Death)

Technology
The Tersurons were able to build castles as well as vast sewer systems which could take centuries to find the way out of. They appeared to do this before the discovery of fire. (NOTVALID: The Curse of Fatal Death)

History
The architect of Castle Tersurus was subject to various bribes by the Ninth Doctor and the Master to make the other fall into traps while anticipating that they would later bribe the architect to do the same.

After discovering fire, all the Tersuran-speaking Tersurons went extinct. (NOTVALID: The Curse of Fatal Death)