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Phylum Cnidaria General Characteristics About 9000 species _____________________ Simple nervous system __________________ Diploblastic organization Endoderm Ectoderm General Characteristics Cont’d• Either tubular or bell shaped • _______________________ • Only animal with cnidocytes • Cnidocytes-specialized stinging cells (on tentacle) • _______________________ • All marine (aquatic) ____________________________ • Cnidarians’ bodies are organized around the gastrovascular cavity, where digestion takes place • GV has a single opening that serves as both mouth and anus 2 Layers of Cells –Diploblastic: •__________________________ –Gastrodermis: lines GV cavity –Epidermis: lines the outside of the body (the skin) • In between the two layers is the _________- a jelly-like substance. Cnidarian Body Wall Stinging Cells • Have Cnidocytes –________________ –Contain nematocysts: barbed thread-like structures inside the cnidocyte that shoots out and can puncture and poison or entangle prey Cnidocyte Feeding • _______________________________ • Inner gastrodermis secretes digestive juices into gastrovascular cavity which digests food and circulates nutrients Feeding Cont. Nervous and Movement •_________________ & sensory receptors •Muscles help in directional movement & capturing prey Life Cycles • Cnidarians have two body forms that are representative of the sexual and asexual life cycles that they undergo. –_______ –Medusa Polyp –_______ –_______ –Usually attaches to a substrate at the aboral end –Oral end is surrounded by feeding tentacles Medusa _________ ________________ Sexual (dioecious) Shaped like an upside-down bowl Tentacles surround the mouth that is housed underneath the bell • When cnidarians display both forms at some point in their lives, they are said to display an __________________________ _________________________ Both sexual and asexual Sexual Gametes released into water Fertilization takes place to create free-swimming planula Asexual By budding Generalized Cnidarian Life Cycle __________________________ • Scyphozoa: Jellyfish • Anthozoa: Sea anemones & Corals • Hydrozoa: Hydra • Cubozoa: Box Jellies Class Hydrozoa • Ex. Hydras • __________________ • Includes hydras, fire corals, and Portuguese Man of War • Display alternation of generations –Polyp –Medusa Class Scyphozoa • True Jellyfish • ___________________________ –Small polyp stage during life cycle _____________________ • Similar to Scyphozoans, except that their medusa is cuboidal • Includes the box jellyfish –1 of the 10 most venomous animals on the planet –Kills 12 people per year Class Anthozoa • Polyps that are flower-like • ___________________ • Includes sea anemones, corals, sea whips, and sea fans
