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Mollusks

Mollusks. Chapter 16. Molluscs are triploblastic which means three tissue layers. II.             Molluscs are coelomates:  a fluid filled body cavity lined by mesoderm.  Have a complete digestive system. 2 Groups of coelomates:. 1.  Protostomes: Molluscs and Annelids

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Mollusks

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  1. Mollusks Chapter 16

  2. Molluscs are triploblastic which means three tissue layers. • II.             Molluscs are coelomates:  a fluid filled body cavity lined by mesoderm.  Have a complete digestive system.

  3. 2 Groups of coelomates: • 1.  Protostomes:Molluscs and Annelids • Spiral, determinate cleavage • The blastopore forms the mouth

  4. 2.    Deuterostomes: echinoderms, chordates • v  Radial, indeterminate cleavage. • v  The blastopore forms the anus.

  5. The coelom may have formed from splitting of the mesoderm or from out-pocketing of the gut.

  6. Phylum Mollusca shares characteristics • III. 8 different classes • Body composed of a head-foot and visceral mass (organ systems) • A mantle – covers visceral mass and may secrete a calcareous shell

  7. Other common characteristics • Bilateral symmetry • Protostome characteristics • A trochophore larva • A reduced coelom • Open circulatory system •     (exception: cephalopods which have a closed       •      circulatory system) • Many molluscs feed via a radula

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