Karnas'koi

The Karnas'koi were vast, winged Great Old Ones. Their language, according to the Doctor "predates history [and is a] language of the Old Time."

History
The Karnas-koi lived on Earth up to six million years ago, 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 requires two keys - one is of crystal and opens the surface Citadel, the other is golden and opens the ocean floor and the centre of the universe, finally and fully releasing the Lurkers.