Plankton.
There are many types of animals and plants in the ocean. The tiny sea plants and animals are called plankton or phytoplankton.
Some plants eat plankton and other small creatures.
Phytoplankton is the small plant life that whales and some other sea life eat. Many other forms of sea creatures eat fish and other sea creatures.
Corals are not plants. They are the colonies of dead creatures called polyps. Their skeletons stack to make coral reefs.
Small single celled plants called 'phytoplankton', seaweeds and sea grasses.
Most crustaceans are omnivorous, as they consume both aquatic plants, like sea weed and small aquatic creatures (Shrimps, small fish etc.) Crustaceans like Lobsters and Crabs.
Sea anemones do not hide, they are plants that small sea creatures hide in from predators, as they sting, but the smaller creatures that hide in them have adapted so they do not feel it much or at all. I would recommend this educational film for you:- Finding Nemo
it was formed by sea plants and creatures
they are called pisces
small fishes
None, the deep sea is in space
They feed on fish and other small sea creatures.