The Ferret is a domesticated relative of the wild Polecat and is sometimes classed as a subspecies and sometimes as a separate, evolved species.
Usual Ferret colouring
The elongated mustelid shape
The Ferret is usually slightly smaller, has a slightly more pointed face, a limited or absent face mask and usually light at the back of its white-bordered ears.
Ferrets also come in a wide range of coat colours, including albino, and can be feral.