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Phylum Mollusca

Phylum Mollusca. 75000 species 2 nd only to Phylum Arthropoda Includes octopuses, oysters, snails, slugs, squids, clams… Divided into 6 classes based on shell and foot. Common Characteristics. Shell ~ tough multilayered structure, for protection or body support

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Phylum Mollusca

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  1. Phylum Mollusca 75000 species 2nd only to Phylum Arthropoda Includes octopuses, oysters, snails, slugs, squids, clams… Divided into 6 classes based on shell and foot

  2. Common Characteristics • Shell ~ tough multilayered structure, for protection or body support • Mantle ~ sheath of tissue that encloses vital organs, secretes its shell and forms its respiratory structures • Visceral hump ~ contains its heart, digestive, and excretory organs, covered by mantle • Foot ~ fleshy, muscular organ used for locomotion • Radula ~ small organ covered with tiny teeth that scrapes up food particles and draws them into mouth. • Trochophore- ciliated larval form

  3. 3 Mollusk Classes • Bivalvia – two shelled mollusks • Gastropoda- stomach footed mollusks • Cephalopoda – head footed mollusks

  4. Clam Nutrition and Digestion • Filter feeders- feed on organic material strained from the water • Bivalves lack a radula • Siphons- tubes used to filter water over the clams body • Palps- pair of lobelike organs surrounding the mouth • Gills and palps secrete a stringy, sticky mucus that catches the food • Cilia move food to the mouth • Digestive system also includes a stomach, digestive gland, intestines, and anus

  5. Class Bivalvia:Two-Shelled Mollusks Clams, oysters, mussels, scallops

  6. Clams Clams secrete shiny material around an irritating foreign object forming a pearl Foot is used for locomotion and burrowing Can also move by rapidly opening and closing shell which causes it to bounce along the seafloor Nervous system including ganglia, nerves, and various sensory organs including as many as 100 simple eyes along the margin of the valve that can detect light and movement Sexual reproduction

  7. Circulation and Respiration • Open circulatory system including a heart and a kidney which filters waste from the blood • Respiratory system including gills- thin walled ciliated structures richly supplied with blood vessels where oxygen and carbon dioxide are exchanged

  8. Class Gastropoda: Stomach-Footed Mollusks Snail, slugs, nudibranchs The foot is immediately below the visceral hump which is where the stomach is located. Nudibranch Videos http://www.youtube.com/watch?v=cJE-LPcwtP8 http://www.youtube.com/watch?v=V6H01cUSpfQ

  9. Nutrition and Digestion • Eats plant material • Scrapes food with tonguelikeradula • Torsion- body develops into twisted, asymmetrical arrangement unique to gastropods, anus is close to anterior region of the body, above the mouth

  10. Mantle cavity • space between the mantle lining, the shell, and the animal’s soft body • Thickly supplied with blood vessels and functions as a lung in respiration Respiration

  11. Locomotion • Lays down a layer of slime • Glides on slime by rhythmical contractions of its muscular foot (10ft per hour)

  12. Series of ganglia around the head region • Pair of eyes at the end of two tentacles • Other receptors for smell, touch, and chemical detection located in the head and foot Response

  13. Class Cephalopoda: Head-Footed Mollusks Octopus, squid, nautilus, cuttlefish

  14. Class Cephalopoda The foot extends from the head region The foot is usually divided and contains suckers Squids eyes are much like mammalian eyes and are capable of very accurate vision. Amazing camouflage and mimicry abilities http://www.youtube.com/watch?v=1VjxvrXGEHk http://www.youtube.com/watch?v=t-LTWFnGmeg http://www.youtube.com/watch?v=3pDVScNCkiI http://www.youtube.com/watch?v=7NQUqR_YpsA

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