Slitheen
Appearance
The Slitheen are a family (ie. brothers and sisters) of aliens appearing in the 2005 Doctor Who episodes Aliens of London and World War Three. They are mentioned also in Dalek. Their home planet is Raxacoricofallapatorius, and they are made out of living calcium. This makes them suceptible to being dissolved by vinegar - similarities to The Wizard of Oz have been pointed out.