Untold is a category of creatures that are not classifiable into any of the other groups.
You might think of bacteria, coral, barnacles, mold, or sea cucumbers.
Bewildered Vat - (added 5 March 2014) - A nasty acidic beast with a hardened bowl to hold it.
Wealdeye - (added 10 October 2015) - A slug with camouflage like tree bark
CfKr9 Animaliaphage (Virus) - (added SOON!) - A four-legged beast that replicates itself within animal hosts.