2011L Lec4 Cnidaria Spr08

2011L Lec4 Cnidaria Spr08 - Phylum Cnidaria-bearing...

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Unformatted text preview: Phylum Cnidaria-bearing stingers (cnidae)- The major lineages of evolution in animals Fundamental evolutionary divergence among Eumetazoa, but based on what? Two phyla exhibit radial symmetry throughout life* *Both are considered the most primitive Eumetazoans Ctenophora : comb jellies Cnidaria : hydroids, jellyfish, sea anemones and corals ~ 10,000 species in the phylum- most are marine - a few freshwater species exist (e.g., the common lab animal, Hydra ) There is no collective common name for cnidarians (jellyfish, corals, sea anemones, and hydroids are common names for the classes) Cnidarians are either solitary or form colonies . coral portuguese man-0-war- Cnidarians derive their name from their stinging cnidocyte cells that are characteristic of the phylum.- Cnidocytes contain organelles called cnidae that eject harpoon- like stinging ( nematocysts ) or adhesive threads. - With the exception of a few herbivorous coral species, most cnidarians are carnivorous. They entangle and poison potential prey using their nematocysts. Some cnidarians - particularly cubomedusan box jellies can be fatal to humans. box jellies QuickTime7 and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTime7 and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTime7 and a TIFF (Uncompressed) decompressor are needed to see this picture. Also, the sting of some corals can harm humans Fire coral Symptoms include severe shooting pain described as a shocklike sensation, and intense joint and muscle pain. Pain may be accompanied by headaches, shock, collapse, faintness, hysteria, chills, fever, nausea and vomiting. Nematocysts (= a stinging cnidum) Cellular organelle Formed within a cnidocyte (cell) A capsule with coiled, inverted thread with spines, toxin Chemotactile cue, explosive thread eversion Osmotic pressure Each cnidocyte has a hair- trigger, the cnidocil , which is usually activated by physical contact causing the cell to burst open and extrude its contents. Physical or chemical contact causes a sudden increase in the permeability of the cell membrane; water rushes in until cell pops open and the cnidum (nematocyst) is forced out. Inside each cnidum (nematocyst) is a coiled, barbed thread which explodes out of the cell. Deployed Nematocysts There are several kinds of cnidae (nematocysts) that are generally grouped in into three functional categories: Volvents have a whiplike end that wraps around spines of prey. Glutinants have a sticky secretion that sticks to the prey. Penetrants have barbs at their tips and penetrate the prey, often injecting a toxin causing paralysis. Cnidae (nematocysts) functions: Prey capture Defense Adhesion Aggression! Although cnidae are unique to the phylum and are the origin of the name Cnidaria, some flatworms and molluscs steal cnidae and use them for defense....
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2011L Lec4 Cnidaria Spr08 - Phylum Cnidaria-bearing...

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