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Mollusks

Mollusks. TSW identify and describe the basic characteristics of mollusks. What is a mollusk?. Soft-bodied animal with an internal or an external shell Very diverse phylum, but all share similar developmental stages

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Mollusks

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  1. Mollusks TSW identify and describe the basic characteristics of mollusks

  2. What is a mollusk? • Soft-bodied animal with an internal or an external shell • Very diverse phylum, but all share similar developmental stages • Many have TROCHOPHORE larvae: free-swimming larval stage of aquatic mollusks

  3. Form & Function • True COELOMS surrounded by mesoderm tissue • Complex, interrelated organ system

  4. Body Plan • 4 Main Parts • FOOT: Muscular, used for crawling, burrowing, & capturing prey • MANTLE: Thin layer of tissue covering the mollusk’s body like a cloak • SHELL: Made of calcium carbonate; has been lost in some groups • VISCERAL MASS: Internal organs

  5. Feeding • Can be herbivores, carnivores, filter feeders, detritivores, or parasites

  6. Feeding Structures • RADULA: Flexible, tongue-like structure to which hundreds of tiny teeth are attached • SIPHON: Tubelike structure through which water enters and leaves the body

  7. Respiration • Aquatic mollusks typically breathe using gills inside their mantle cavity

  8. Circulation • Oxygen & nutrients are carried to all parts of a mollusk’s body via an open or closed circulatory system • OPEN: Blood is pumped through vessels by a simple heart sinuses gills  heart • Works best in slow-moving mollusks (snails & clams) b/c their demand for oxygen is low

  9. Excretion • Cells release nitrogen-containing waste into the blood in the form of ammonia • Nephridia: tubular structures that collect fluids from the coelom and exchange salts and other substances with body tissues as the fluid passes along the tubules for excretion.

  10. Response • Complexity varies depending on the species

  11. Movement • Rippling motion of the foot (snails) • Jet propulsion (octopi)

  12. Reproduction • Sexually via external fertilization • Some have internal fertilization • Some are hermaphrodites

  13. Groups of Mollusks • Divided into three main groups depending on the characteristics of the foot and shell • Gastropoda • Bivalvia • Cephalopoda

  14. Gastropoda • Gastropods • Shell-less or single-shelled • Move using a muscular foot on the ventral side • Examples: Pond snails, sea butterflies, sea hares, limpets, & nudibranchs

  15. Bivalvia • Bivalves • 2 shells that are held together by 1 or 2 powerful muscles • Most stay in one lace much of the time • Many are filter feeders, but some use long, muscular extensions to collect food

  16. Bivalve: Examples • Clams, oysters, mussels, and scallops

  17. Cephalopoda • Cephalopods • Soft-bodied, head is attached to a singular foot that is divided into tentacles or arms • Most active of all mollusks • Small internal shell or no shell at all • Numerous, complex sense organs

  18. Cephalopods: Examples • Octopi, squid, cuttlefish, nautilus

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