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Cnidarians & Ctenophorans 1 CNIDARIANS Phylum Cnidaria • About 9000 species • Most are marine (jellyfish, coral, sea anemones, Portuguese man-of war) • Hydras are found in freshwater • All have arm-like tentacles Cnidarian Characteristics • Radial symmetry • Hollow gut -Gastrovascular cavity has single opening (serves as both mouth and anus) • Two tissue layers (diploblastic) • Outer epidermis and inner gastrodermis Cnidarian Characteristics •Either tubular or bell shaped •Tentacles surround mouth •Only animal with cnidocytes (stinging cells) found in the tentacles •Nematocyst – coiled, harpoon-like stinger inside cnidocyte that shoots out Cnidarian Characteristics •Cnidocytes contain poison to paralyze prey •Tentacles bring food into mouth •Inner gastrodermis secretes digestive juices into gastrovascular cavity which digests food and circulates nutrients Extracellular Digestion Food digested outside of cells Cnidarian Systems •Have a simple nerve net & sensory receptors •Muscles help in directional movement & capturing prey mesoglea-filled bell tentacles Jellylike mesoglea between two cell layers supports cnidarian Cnidarian Diversity • Scyphozoans: Jellyfish • Anthozoans: Sea anemones Corals • Hydrozoans: Hydra • Cubozoa Box Jellies Cnidarian Diversity Coral polyps Sea Anemone Jellyfish Coral polyps Anthozoans Anthozoan Characteristics Sea Anemones Brightly colored & Resemble flowers Solitary polyps Feed on invertebrates & fish Corals Most are colonial Build limestone case Live as polyps in their case Sea Anemones & Coral • Exist only as Polyps • Clownfish live in anemone tentacles • Corals build a limestone case which build up & form reefs ANEMONE CORAL Hydrozoans Hydra •Exist only as polyps •Reproduce by budding •Freshwater only •Form resistant zygotes when environment is bad •Move by somersaulting with tentacles Hydra Portuguese man-of-war • Colonial Hydrozoan (not a single organism • Tentacles sting prey such as fish & humans • Polyps in colony feed • Has gas-filled air float Cubozoans Box JellyFish Scyphozoans Scyphozoan Characteristics Jellyfish • Medusa is dominant body form • Go through small polyp stage during life cycle •Stinging tentacles •May live close to shore or the open ocean Parts of a Jellyfish Jellyfish Life Cycle 24
