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Phylum Mollusca Mollusk General Characteristics

Phylum Mollusca Mollusk General Characteristics. Are a very diverse phylum Most have a specific type of larvae ( trochophore ) Are all soft-bodied with an internal or external shell. Body Plan. Have a coelom (true body cavity), with a one way digestive system

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Phylum Mollusca Mollusk General Characteristics

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  1. Phylum MolluscaMollusk General Characteristics • Are a very diverse phylum • Most have a specific type of larvae (trochophore) • Are all soft-bodied with an internal or external shell

  2. Body Plan • Have a coelom (true body cavity), with a one way digestive system • Are bilaterally symmetrical with 4 basic body parts: • Foot- usually contains mouth and feeding parts • Mantle- tissue layer that covers most of the body • Shell- may be internal or external • Visceral Mass- contains the internal organs

  3. Mollusk Body Plan

  4. Feeding • Many contain a tongue shaped structure called a radula that has hundreds of teeth • Some have jaws surrounding radula • Others use gills to filter-feed (eg bivalves)

  5. Respiration • Aquatic mollusks use gills (ctenidia) • Terrestrial mollusks use mantle cavity (adapted to resemble a lung)

  6. Internal Transport • Many have an open circulatory system • Faster moving mollusks have a closed circulatory system

  7. Elimination and Excretion • Solid waste leaves through anus as feces • Nitrogen waste is excreted by nephridia

  8. Response • Greatly varies within the phylum • Many have simple nervous systems (eg. clams) • Some have highly developed nervous systems with a well developed brain (eg. octopuses) • Octopuses have well developed eyes

  9. Reproduction • Sexes are separate in most • Fertilization is external in most

  10. Major Classes • Gastropods- have stomach next to foot • Move via a muscular foot on ventral side • Have one shell, a reduced shell, or no shell • Snails and slugs

  11. Major Classes • Bivalves- have two shells • Held together by one or two powerful muscles • Most are sessile • Clams, oysters, mussels, scallops

  12. Cephalopods- have head next to foot • Foot is divided into tentacles • Most have small internal shells or no shells • Octopuses, squids, cuttlefish, nautiluses

  13. 4. Polyplacophora- chitons - bear a number of plates

  14. 27-1 Section Review • Mollusks are soft bodied animals with an internal or external shell. • Characterized by having a trochophore larvae during life cycle

  15. 2. Effect of Mollusks on Humans • Mollusks as food- snails, clams, oysters, scallops, squid, etc (can cause illness during red tides). • Mollusks as pests- snails and slugs damage crops, shipworms drill through wood • Used in biological research- eg. Cancer research

  16. 3. Uses of radulla • Herbivores use radula to scrape algae off rocks and twigs, or to eat plants • Carnivores use radula to drill through the shell of other animals • Cone shells use radula as poisonous darts

  17. 4. Protection • Some burrow or hide • Some have well developed brains and rely on senses and intelligence to avoid predation • Some are fast swimmers e.g. sea butterfly or flap their shells eg. scallops • Some rely on tasting bad (or poisons) to predators eg. Snails and slugs • Some release ink eg. Squid • Some are able to change colours to blend into surroundings eg. Octopi

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