The cnidarians have a very simple construction but contain some internal organs as well as a primitive neural system. Cnidarians come in many sizes but basically only in two shapes. Either as benthic polyps that look like flowers or pelagic medusa that look like parachutes. Many species go through both of these stages during their life. The main groups of cnidarians are jellyfish, sea anemones, corals and hydrozoans.
Hydrozoans are common as both polyps and small medusa. The polyps form colonies similar as corals. The hydrozoan colonies are soft and form what to the naked eye looks like vegetation in between other sessile animals or kelp. These are of course animals, not plants.