Karnas'koi

The Karnas'koi — or "lurkers" — were vast, winged Elder Gods. Their language, according to the Seventh Doctor, "predate[d] history [and was a] language of the Old Time."

History
The Karnas-koi lived on Earth in its distant past, but their society collapsed and four of its mightiest went into a self-induced sleep within their Citadel as it sank beneath the waves. On the ocean floor they had been contained by a "sleeping chant" and their release required two keys — one was of crystal and opened the surface Citadel, the other was golden and opened the ocean floor and the centre of the universe, finally and fully releasing the Lurkers. (AUDIO: Lurkers at Sunlight's Edge)