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Related Flashcards
Cards In This Set
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Spell the Phylum
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Phylum Mollusca
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Widespread in most environments: ____ (all classes), freshwater (some ____ and ___) and even _____ (some gastropods)
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Marine; gastropods and bivalves; terrestrial
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There are 7 extant molluscan classes, what are they and what do they include in each
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Bivalvia (clams, mussels), Gastropoda (snails, slugs), Cephalopoda (octopus, squid, cuttlefish, nautilus), Scaphopoda (tusk and tooth shells), Polyplacophora (chitons), Monoplacophora, Aplacophora
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Describe the mollusc ancestry
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Uncertain but they are protosomes, schizocoelous, and have spiral determinate cleavage
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What are the characteristics of molluscs
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Triploblastic, organ level organization, bilateral symmetry, eucoelomate but coelom reduced to pericardium and gonadial cavity, protostome, trocophore and veliger larvae as well as some with direct development
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What are the 4 distinct body plan characteristics of molluscs
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Head, muscular foot (from ventral body wall), visceral mass, and mantle (from dorsal body wall)
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What structures are in the head and foot
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Sensory organs and muscles
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What structures are in the visceral mass
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Digestive, reproductive and circulatory organs
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What is the function of the mantle and what does it contain
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Secretes the shell (if present) and the mantle cavity contains gills or lungs
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What is HAM
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Hypothetical Ancestral Mollusc=an abstraction derived from comparative morphology and embryology
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 Find the outer periostracum, prismatic layer, nacreous layers and the free and attached zones of the mantle |
 Find them |
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How are pearls created
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Mollusc deposits layers of nacre around an irritant that gets lodged between the mantle and shell
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 Find the Coelom, mantle, mouth, radula, foot, anus, mantle cavity, gill, and shell |
 Find them |
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How were each of the molluscan classes derived from HAM
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Scaphopoda= ventral shell fusion
Gastropoda= torsion of body and coiling of the shell Polyplacophora= shell consists of 8 plates Cephalopoda=lobed foot, highly developed head, shell reduced or lost Bivalvia= bivalved shell, dorsal hinge and adductor muscles |
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Describe gastropod torsion
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•
an
unusual developmental process that is peculiar to gastropods and apparently a
primitive feature in this class
• rotation of visceral hump brings mantle
cavity anteriorly - to provide protection to head?
• see a twisting of the visceral mass
through a 180°
rotation during development:
• 1st 90° rotation usually occurs at the
veliger (early larval) stage
• 2nd 90° rotation usually takes longer
and occurs later
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