Cnidaria (Coelenterates, such as Jellyfish and Sea Anemones) Stings By Robert A Barish, MD, MBA, University of Illinois at Chicago; Thomas Arnold, MD, Department of Emergency Medicine, LSU Health Sciences Center Shreveport Reviewed / Revised Jan 2022 | Modified Sep 2022 View Patient Education Symptoms and Signs Treatment Topic Resources Jellyfish Cnidaria include the following: Corals Sea anemones Jellyfish (including sea nettles) Hydroids (eg, Portuguese man-of-war) Cnidaria are responsible for more envenomations than any other marine animal.