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Phylum Cnidaria • About 9000 species • Most are marine (jellyfish, coral, sea anemones) • Hydras are found in freshwater Acad Body Plan • Radial symmetry • Gastrovascular cavity Hollow gut with single opening (serves as both mouth and anus) • Referred to as a twoway digestive system • The mouth is surrounded by flexible tentacles Body Plan • Two tissue layers: outer epidermis and inner gastrodermis • A jellylike material called mesoglea is between the layers Two Main Body Plans of Cnidarians UPRIGHT TENTACLES TENTACLES HANG DOWN epidermis Polyp mouth gastrodermis Medusa Motile Swimmers Sessile Filter-feeders Feeding & Digestion •Tentacles surround mouth •Cnidocytes (stinging cells) found in the tentacles; give defense and capture prey •Some work like a harpoon •Some work like a whip •Nematocyst – coiled, harpoon-like stinger inside cnidocyte that shoots out Feeding & Digestion •Cnidocytes contain poison to paralyze prey •Tentacles bring food into mouth •Inner gastrodermis secretes digestive juices into gastrovascular cavity; digests food and circulates nutrients •Waste is expelled back through mouth Nervous System •No central nervous control •Nerve net & sensory receptors •Muscles help in movement, reaction to stimuli, & capturing prey Reproduction • Many can regenerate (regrow) lost body parts through mitotic cell division (asexual) • Many also reproduce asexually by budding Reproduction • Most reproduction is sexual • Many alternate between medusa and polyp form in a reproductive life cycle Cnidarian Classes • Hydrozoans: Hydra Portuguese man-of-war • Cubozoa: Box Jellies • Scyphozoans (means “cup animals”): Jellyfish • Anthozoans (means “flower animals”): Sea anemones Corals Hydrozoans Hydra •Exist only as single polyps •Freshwater only Portuguese man-ofwar • Colonial mix of polyps and medusas (not a single organism) Cubozoans Box JellyFish Sea Wasp – can be deadly Scyphozoans - Jellyfish Anthozoans: Sea Anemones & Coral ANEMONE CORAL Phylum Ctenophora • Called “comb jellies” • All marine animals with radial symmetry • Approximately 100 species • May be spherical, ovoid, or elongate in appearance • Bioluminescent Beating Cilia Ctenophore: Comb Jelly Ctenophoran Characteristics • Radial symmetry • Have eight plates of fused cilia that resemble combs • Move by beating cilia • Most of the body is a jelly-like substance called mesoglea • Body & tentacles covered with sticky mucus to catch prey