Gastropod

The Gastropods, led by Mestor, devoured the vegetation of the planet Jaconda.



Biology
The Gastropods resembled humanoid slugs. They left a sticky trail. Unspeaking, they followed the commands of Mestor, leaving one to assume they made only vestigial intelligence. Mestor planned to make the Jaconda's sun go supernova so as to scatter Gastropod eggs into space. (DW: The Twin Dilemma)

Abilities
Gastropods had a form of mental powers which they could use to either kill individuals or take over their mind and communicate through them. They could also communicate telepathically. (DW: The Twin Dilemma)

History
Jaconda, once a verdant paradise, became a despoiled wasteland once the Gastropod appeared and made the Jacondans slaves in their own world. The Sixth Doctor killed Mestor and ended the reign of the Gastropods. (DW: The Twin Dilemma)

Behind the scenes

 * According to The Brilliant Book 2012, a non-canonical REF book; there was a fossilised Gastropod in Dr Henry Fizzog's Museum of the Macabre on Sardicktown.
 * The name for this monster obviously derives from Gastropods, the biological class of slugs and snails.