Oceanphere

On the Aqua planet, oceanpheres were patches of invisible liquid in which fish and Aquamonsters swam, making the illusion that they were in flight. These creatures could not survive out of the liquid.

When the First Doctor, Ian Chesterton and Barbara Wright landed on the Aqua planet, they were caught up in the oceanpheric currents. Once in, an Aquamonster attempted to eat Barbara. Fortunately, the three travellers soon fell out of the oceanphere; since Aquamonsters could not survive out of the oceansphere, it left Barbara alone. (COMIC: Dr. Who on the Aqua Planet)