cross section of hydra polyp and close-up of cnidocyte explosive cell that contains the toxin

anatomy animal animals asexually biology blue body budding cell cnidaria cnidocyte coral design diagram education element fresh freshwater hydra hydroid hydrozoa illustration jelly jellyfish lessons macro marine microbiology microorganism model mouth nature nematocyst ocean organism ovary pond predator protozoa reef regeneration reproduce reproduction research scheme school science scientific sea still structure tentacles tube underwater vector vulgaris water white wildlife