Flooded World

The episode is set in shallow seas of Paris, 100 million years into the future. The episode focuses on three species which all live together: (1) Ocean Phantom, a type of portuguese man-of-war that can grow to ten metres in diameter; (2) Reef Glider, a descendant of the sea slug which hunts ocean phantoms. The young, however, are prey to the ocean phantom; (3) Spindle Trooper, sea spiders that live in chambers on the Ocean Phantom and protect it from danger. The Ocean Phantom in return feeds it. This episode focuses on the extinction of the coral reefs and their replacement with red algae reefs. It shows how this food chain works and how the animals have evolved together. It also shows how Ocean Phantoms can be ripped apart by a severe storm but still carry on living.