Mollusca

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Mollusca

  1. 1. Mollusca
  2. 2. Core Concepts <ul><li>Mollusks, Phylum Mollusca, are-soft bodied animals that have an internal or external shell </li></ul><ul><li>Grouped together due to similar developmental pattern </li></ul><ul><li>Most of them have a special kind of ciliated larva called a trocophore that swim in open water and feed on tiny floating plants (phytoplanktons) </li></ul>
  3. 3. <ul><li>Trocophore larvae are seen in both mollusks and annelids which indicate that they evolved from a common ancestor (although segmentation was lost early in the evolution of mollusks) </li></ul>
  4. 4. <ul><li>Most adult members have: </li></ul><ul><ul><li>bilateral symmetry </li></ul></ul><ul><ul><li>Open circulatory system (except cephalopods) </li></ul></ul>
  5. 5. <ul><li>Body plan consists of four parts: </li></ul><ul><ul><li>Muscular foot </li></ul></ul><ul><ul><li>Mantle </li></ul></ul><ul><ul><li>Shell </li></ul></ul><ul><ul><li>Visceral mass </li></ul></ul>
  6. 6. <ul><li>Divided into 7-9 classes </li></ul><ul><ul><li>3 major classes </li></ul></ul><ul><ul><ul><li>Class Gastropoda (snails, nudibranchs, slugs) </li></ul></ul></ul><ul><ul><ul><li>Class Pelecypoda (clams, oysters, mussels, scallops) </li></ul></ul></ul><ul><ul><ul><li>Class Cephalopoda (Squids, octopuses, cuttlefish) </li></ul></ul></ul>
  7. 7. Keywords <ul><li>Mollusca Malacology Pelecypoda </li></ul><ul><li>Gastropoda Cephalopoda mantle cavity </li></ul><ul><li>Trocophore larva mantle gills </li></ul><ul><li>Muscular foot internal/external shell </li></ul><ul><li>Visceral mass radula filter-feeder </li></ul><ul><li>Sinuses nephridia ganglia </li></ul><ul><li>Statocyst ocelli (eyespots) </li></ul>
  8. 8. General Characteristics <ul><li>Diversity: more than 150, 000 known species </li></ul><ul><li>Molluscus= soft </li></ul><ul><li>Soft-bodied animals with a muscular foot that usually contains the mouth and other structure associated with feeding </li></ul><ul><li>Mantle </li></ul><ul><ul><li>Thin delicate cloak-like tissue layer that covers most of the mollusk’s body </li></ul></ul>
  9. 9. <ul><li>Shell- calcareous (CaCO 3 ) secreted by mantle </li></ul><ul><li>Visceral mass- beneath the mantle </li></ul><ul><li>Mantle cavity- extension of the mantle; contains the gills, anus and excretory pore </li></ul><ul><li>Organ-system level of organization </li></ul>
  10. 10. <ul><li>Most adults have bilateral symmetry </li></ul><ul><li>Complete digestive system </li></ul><ul><li>Coelomate </li></ul><ul><li>Triploblastic </li></ul><ul><li>Open circulation (except cephalopod) </li></ul><ul><li>Classification: type of foot and kind of shell </li></ul>
  11. 11. Digestive system <ul><li>Mostly herbivores, carnovores, filter-feeders, few are detritus feeders and parasites </li></ul><ul><li>Radula- used for rasping or scraping or drilling to eat </li></ul><ul><li>Sharp jaws- use by octopuses to break shells </li></ul><ul><li>Use of poison </li></ul><ul><li>Filter-feeders- use of feathery gills (sometimes with mucus) </li></ul>
  12. 12. Respiration <ul><li>Use of gills or cutaneous respiration (skin) </li></ul><ul><li>Land snails and slugs- use mantle (High SA, rich in blood vessels) </li></ul>
  13. 13. Circulatory System <ul><li>Simple heart </li></ul><ul><li>Hemolymph (blood + interstitial fluid) </li></ul><ul><li>Open circulation (sessile) </li></ul><ul><ul><li>Blood flows into spaces called sinuses </li></ul></ul><ul><li>Close circulation (fast-moving) </li></ul>
  14. 14. Excretory System <ul><li>Nephridia- organ used to remove ammonia in their system </li></ul>
  15. 15. Nervous System <ul><li>Nerve ring- surrounds the esophagus </li></ul><ul><ul><li>Where nerve cords extend </li></ul></ul><ul><li>Simple nervous system (inactive bivalves) </li></ul><ul><ul><li>Statocysts- balance </li></ul></ul><ul><ul><li>Ocelli- eyespots </li></ul></ul><ul><li>Complex nervous system (intelligent predators) </li></ul>
  16. 16. Reproduction <ul><li>Separate sexes in most mollusks </li></ul><ul><li>Many hermaphrodites </li></ul><ul><li>External fertilization </li></ul><ul><li>Internal fertilization (tentacled mollusks, snails) </li></ul><ul><li>Sequential hermaphroditism </li></ul><ul><ul><li>Change of sex depending on environmental factors </li></ul></ul>

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