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Phylum Cnidaria (Coelenterata) General Characteristics Has only one opening Has 2 tissue layers – Epidermis – Gastrodermis – Mesoglea (mostly jellifish) Body Form- Medusa Bell-shape u Free swimming u Mouth and tentacles face down u Body Forms- Polyp n n n Tube-shape Usually sessile Mouth and tentacles are face up Polyp vs. Medusa General Body Parts ► Mouth § Surrounded by ring of tentacles § Oral disc surrounds mouth Tentacles Contain cnidoblasts Cnidoblasts contain nematocytes Stinging structures “Harpoon –like” Can discharge to sting One of the fastest known cell movements Can contain poison Can be sticky or tangle prey Response – Nerve net Simple nervous system with no brain Limited movement of prey from tentacles to mouth Gastrovascular Cavity n A blind-sac where food is digested Pedal Disc Pedal disc Polyps only – Used for attachment. Skeleton § Coral only § Made of calcium carbonate (CaCO3) § Forms reefs § Very important ecosystem Reproduction- Sexual ► Sperm and egg (mostly separate sexes) Reproduction- Asexual Budding (mostly in polyp form) Reproduction- Alternation of Generation Class Scyphozoa- Jellyfish About 200 spp. Made up of gel-like substance (mesoglea) Tend to have separate sexes Sex cells visible through bell More Scyphozoa n Move by pulsating bell n n n n n Not strong swimmers Vertical migration Fastest of the plankton Top: Moon jelly Bottom: Lion’s mane Class Hydrozoa About 3000 spp. May live alone or in colonies – Colonies have many individuals that has specialized jobs and can no longer live alone – Top: Portugese Man of War – Bottom: Hydra Class Anthozoa Largest class About 6000 sp. Sea Anemones No skeleton Sessile Single polyps (larger) Stinging cells around mouth Corals n n n Colonies Skeleton (CaCO3) Zooanthalle (below) n Photosynthetic friend Anthozoa Examples Top: Northern red anemone Bottom: Northern Star coral Cnidarian Overview