Horda
From TARDIS Index File, the free Doctor Who reference.
Horda were small predators native to Leela's home planet. They resembled long, armoured fish with large heads. Horda were forced to crawl around the forest floor slowly. Though not especially fast, they could strike quickly and ten of them could devour a Human's arm in seconds.
The Sevateem had a test using these horda. The criminal is put on a board above a pit of hordas. This board is pulled into the walls with a boulder attached to a rope. The criminal has to break the rope with a crossbow, stopping the board and saving their life. (DW: The Face of Evil)
