Mirrorite

From the planet Shinnus the Mirrorite are large flat savage predators capable of flight, with shiny reflective backs and savage teeth around a gaping mouth located on its underbelly. They stalk their prey by lying low and creeping up when the prey has become weak enough not to be able to fight back. It has evolved to allow itself to split into two halves each although a little weaker than the whole is capable of independent movement and hunting.

It is unknown how a Mirrorite came to be found in the Australian outback in 1943, but the creature was captured and returned home by the Eleventh Doctor and Amy Pond

(DWAM: Seeing Things)