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Phylum: Cnidarians What is a Cnidarian? A cnidarian is an invertebrate It uses stinging cells to capture prey Examples: – Jellyfish – Corals – Sea Anemones Body Structure All cnidarians have the following characteristics: – Radial symmetry – A hollow central cavity – Tentacles with stinging cells However, cnidarians can have one of 2 different body plans. – Polyp – Medusa Body Plans Polyp – Mouth opens at top – Vase-shaped – Attached to a surface – Examples: Hydra, Sea anemone, Coral Medusa – Mouth opens down – Tentacles point down – Adapted for a swimming life – Examples: Jellyfish Activity: Color Code a Cnidarian Endoderm Tentacle Jelly-like layer (Mesoglea) Ectoderm Tentacle Obtaining Food Stinging cells inject venom which paralyzes the prey – THINK! – Why are clown fish resistant to the toxins given off by sea anemones? Tentacles pull the prey into the mouth Digestion happens in the body cavity Waste is expelled back out through the mouth Movement Cnidarian movements are directed by nerve cells that spread throughout the cnidarians body like a basketball net Jellyfish swim through water Hydras can be found in freshwater and turn somersaults or use their tentacles to move – Watch these Hydra Movies http://micro.magnet.fsu.edu/optics/olympusmicd/galler ies/moviegallery/pondscum/coelenterata/hydra/index.h tml Sea anemones stretch out, shrink down, and bend slowly from side to side Reproduction Asexual – Budding is most common in hydras, corals, sea anemones where these polyps just pull apart forming two new polyps. Sexual – Can occur during the life cycle of certain cnidarians such as the jellyfish Life Cycle of A Jelly Fish Life on a Coral Reef Coral polyps produce a hard, stony skeleton around its soft body once attached to a hard surface. Coral polyps then continue to reproduce asexually Over time, reefs build up from the sea floor and make great homes for other sea life Video Quiz Watch the following clip: – Coral Ecosystems (5:59) There will be a short video quiz following the clip. Make sure to take good notes! You can use your notes for the video quiz!