On the underside of the dome-shaped or bell-shaped body, lies the mouth of jellyfish that are surrounded by the tentacles. So, what do jellyfish eat? They are carnivores that feed on small marine organisms, zooplanktons, comb jellies, crustaceans, and at times, other jellyfish. After assimilation of useful nutrients, the waste products are expelled out from the mouth. The predators of jellyfish include sun fish, sea turtles, spade fish, and larger marine organisms.