Slyther

Slythers were large, tentacled blob-like creatures native to Skaro. During the 22nd century Dalek invasion of Earth, the Black Dalek used a Slyther to guard the Bedfordshire mines at night, where it killed and ate anything it found. After it attacked a small group of humans consisting of Ian Chesterton, Larry Madison, Wells, and Ashton (killing the latter), Ian hit it with a rock, causing it to fall down a pit to its death. (DW: The Dalek Invasion of Earth)

The Daleks used Slythers during their assault on Lan Beta. (NA: Parasite)

Parents alive during the Dalek invasion of Earth used stories of Slythers to scare their children into behaving over 30 years after the events of the invasion was stopped. (BFA: An Earthly Child)

A different looking Slyther is seen in the Graphic Novel The Only Good Dalek