At the bare surface, Cnidarians are invertebrate marine animals with the ability to sting (Jellyfish). They usually aren't anchored to anything, they free float in the water. Their medusa shape and tentacles allow them to free swim in the water. Their body is a sealed bell with a hole at the very bottom, which contracts and forces water out to move. Their tentacles have stinging cells (nematocysts) to paralyze their prey and eat them. Typically they prey on zooplankton, and are preyed upon by sea turtles, sunfish, and spade fish.