Aquamonster

Aquamonsters are fish like creatures native to the Aqua planet. They can only live in the planet's oceanpheric currents.

When the First Doctor, Ian Chesterton and Barbara Wright, Ian noted that he saw a fish fly. In reality there are patches of invisible liquid which the fish swim which move across the planet. However the oceanpheric current ended up catching up to the trio in which an aquamonster attacked Barbara. However as they fell out of oceansphere the aquamonster had no choice but to let her go for it could not live outside of its liquid patch. (COMIC: Dr. Who on the Aqua Planet)