cnidaria & platys

cnidaria & platys - All other metazoans are separated from...

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All other metazoans are separated from Porifera by more complex body form. The first of these are the Cnidarians (Radiata). Porifera Cnidaria Platy- Nematoda Annelida Arthropoda Mollusca Echino- Chordata helminthes dermata levels of cell & tissue organization fundamental symmetry and number of germ layers development pattern the nature of the body cavity presence or absence of a body cavity Protostoma Deuterostoma Eucoelomates Pseudocoelomates other Bilateria Acoelomates Protistan ancestor Eumetazoa Parazoa Bilateria Radiata CNIDARIANS: phylum Cnidaria ("thread-bearers") About 9,000 species, mostly marine (a few in fresh water). TISSUE level of organization: cells organized into specialized tissues, sometimes approaching organs (groups of different tissues with common function) DIPLOBLASTIC --two fundamental cell layers R adial symmetry around oral-aboral axis. Support via hydrostatic skeleton (trapped fluid) or viscoelastic skeleton . Hydrostatic: deformable but not compressible Viscoelastic: deformable but "springy” (elastic), not compressible Sessile and attached, or floating in water -- some swim fairly actively (have contractile non-mesodermal “muscle” cells) Diploblastic animals Cnidarians have a characteristic and unique cell type, the cnidocyte. Cnidocytes are stinging cells with special organelle, the nematocyst. cnidocyte Cnidocil “trigger” Nematocyst, coiled inverted in ‘vacuole’ filled with toxin When cnidocil trigger is touched, or certain chemicals are present, nematocyst discharges by rapidly inverting outwards under pressure: Diploblastic animals A closer look at a discharging nematocyst shows sophisticated mechanism: Rapid projection; thread is ‘fired’ into the target at high speed barbs help dig into target and fix the thread into place propulsion is from high- pressure toxin , which is injected into target can be very powerful; hemolytic or neurotoxic; may be painful or fatal to humans in a few species (box jellies from Australia) target Extended barbs Folded barbs Diploblastic animals
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Polyp form sessile, attached to substrate at aboral end • if mouth closed, water is trapped in gastrovascular cavity • circular and longitudinal ‘muscles’ put pressure on trapped water • tentacles catch food; Oral end Aboral end Epidermis Gastrodermis tentacles Combined mouth and anus Gastrovascular cavity Largely acellular mesoglea simple nerve net and some coordination Diploblastic animals Cnidarians have two basic body forms (quite similar). Both built around two cell layers and hydrostatic or viscoelastic skeleton. Polyp form sessile, attached to substrate at aboral end • if mouth closed, water is trapped in gastrovascular cavity Oral end Aboral end Epidermis Gastrodermis tentacles Combined mouth and anus Gastrovascular cavity Largely acellular mesoglea simple nerve net and some coordination Diploblastic animals • Water is deformable but not
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This note was uploaded on 04/17/2008 for the course BIO 005b taught by Professor Chappel during the Spring '07 term at UC Riverside.

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cnidaria & platys - All other metazoans are separated from...

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