<span>All planets revolve around the sun. - Incorrect. There are many planets that revolve around other stars.
</span>
<span>I believe the answer is: clownfish/anemone
Clownfish is very territorial in nature. So, when they hide within the anemone, the clownfish would prevent smaller fishes from eating the anemone. In return, the anemone would prevent the bigger fish from reaching the clownfish when they hide in it.</span>
primary division of the sea, which includes the whole mass of water subdivided into neritic and oceanic zones; also pertaining to the open sea (open water)