Cnidaria

Cnidarians are animals unique to the aquatic and marine environment, characterised by the presence of cells capable of injecting more or less powerful venom upon contact. They have a free-form shape (jellyfish) or a fixed shape (coral, sea anemone). Polyps are cylindrical with a mouth surrounded by tentacles on the upper part of the animal. Most feed on animal plankton (zooplankton), small animals or plant plankton (phytoplankton).