Crustian

The Crustians were an intelligent race of turtle-like creatures. The sons of Grekk viewed them and all other intelligent life forms on their planet as vermin, and had vowed to exterminate them all. They accused the First Doctor of being a Crustian spy and had him imprisoned in the Pit, where a Crustian prisoner told them about Deemon. The Doctor converted a sustenance unit into a radio transmitter and asked the other Crustians for rescue, knowing that the transmission would be detected by the sons. The Crustian was freed, along with all the other prisoners, when the sons of Grekk fell into the trap they had made. (PROSE: The Sons of Grekk)