Hath

Russell T Davies said that they would be the main monster for the episode The Doctor's Daughter

Myths and rumours
It is rumoured the Hath are red bubbles that communicate through expanding and letting out smaller bubbles. It is also rumoured one of them will kill Jenny at the end of the episode.

continuity
In the comentary for the last of the time lords David tenant jokes on having an enemy that will be a ball on a stick this enemy may be like that!