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Phylum Cnidaria Cnidarians Include Hydras, jellyfish, sea anemones & corals Radially symmetrical Acoelomate Two basic forms: –Polyp: Cylindrical form which attach bases to substratum –Medusa: Flattened, mouth down version of the polyp. Moves freely Forms of Cnidarians Body Plan Basic Body Plan: Has an outer epidermis Has an inner gastrodermis which forms a gastrovascular cavity Has a middle "jelly filled" layer called mesoglea Cnidocytes Cnidarians are predators which have tentacles possessing batteries of special cells called Cnidocytes Cnidocytes contain special stining capsules called nematocysts. When triggered, these cells shoot out a discharge thread which can entangle and/or poison it's intended prey Reproduction – Reproduction can occur sexually by fertilization of egg and sperm forming larvae. – Reproduction can also occur asexually through budding 3 Major classes – Class Hydrozoa: Hydras – Class Scyphozoa: Jellyfish – Class Anthozoa: Anemones and corals Class Hydrozoa: The Hydras Polyp phase is dominant Generally microscopic Generally freshwater Class Scyphozoa: The Jellies Generally refered tro as jellies Medusa stage is dominant Come in a variety of forms Aggressive predators, and can be dangerous to humans Jelly Portugese Man-o-war Class Anthozoa: Anemones & Corals Appear like plants but are animals. Polyp form is dominant. Corals build calcium shells to protect themselves Anemone – Have symbiotic relationship with algae. Can build extensive masses which can form land masses. Coral Polyps Coral Reefs Clownfish living in An anemone
