Phylum Mollusca

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Phylum Mollusca
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Phylum Mollusca

• Protostomes
• Lophotrochozoan group
• Eucoelomates (coelomates)

Tridacna gigas
Tridacna squamosa
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Phylum Mollusca

• Soft Bodied
• Shelled
• Some without
• Cephalization
• Sensory organs
• Mouths
• Body Divisions
• Visceral Mass
• Head-Foot
• Mantle

Tonicella lineata
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Phylum Mollusca
Octopus briareus

• Complete digestive tract
• Digestive glands
• Specialized feeding structures
• Circulatory system
• Heart (2 chambers)
• Open system in most groups
• Closed in cephalopods
• Coelom restricted to pericardium in most cases

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Phylum Mollusca

• Advanced nervous system
• Brain
• Sensory organs
• Eyes (simple and camera)
• Sensory papillae
• Excretory system
• Kidney-like nephridia
• Reproduction
• Monoecious and dioecious
• External development
• External internal fertilization

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Mollusc Phylogeny

• 50-80K extant species
• 40K extinct species
• Fossil records from precambrian period of
  proterozoic eon (gt570my BP)

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Mollusc Phylogeny

• Mantle secreting shell
• Muscular foot
• Chambered heart

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Mollusc Taxonomy
Chiton tuberculatus lives in the rocky intertidal
zones eat algae with its radula 8 shell plates

• Major classes
• Polyplacophora
• Chitons

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Mollusc Taxonomy
Atlantic tritons trumpet (Charonia variegata)

• Major classes
• Polyplacophora
• Gastropoda
• Subclasses
• Prosobranchia
• Shelled marine gastropods

Tiger cowrie (Cypraea tigris)
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Mollusc Taxonomy
Spotted sea hare (Aplysia dactylomela)

• Major classes
• Polyplacophora
• Gastropoda
• Subclasses
• Prosobranchia
• Opisthobranchia
• Sea slugs (marine)

Phidiana hiltoni
zebra sea goddess(Hypselodoris zebra)
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Mollusc Taxonomy
Helminthoglypta walkeriana

• Major classes
• Polyplacophora
• Gastropoda
• Subclasses
• Prosobranchia
• Opisthobranchia
• Pulmonata
• Terrestrial snails/slugs
• Freshwater snails

Giant banana slug (Ariolimax columbians)
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Mollusc Taxonomy
Bay scallop (Aequipecten irradians)

• Major classes
• Polyplacophora
• Gastropoda
• Bivalvia
• Clams, oysters, mussels, scallops

Edible mussels (Mytilus edulis)
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Mollusc Taxonomy
Giant cuttlefish (Sepia latimanus)

• Major classes
• Polyplacophora
• Gastropoda
• Bivalvia
• Cephalopoda
• Octopus, squid, nautilus

Octopus sp
Nautilus sp
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Mollusc Taxonomy

• Major classes
• Polyplacophora
• Gastropoda
• Bivalvia
• Cephalopoda
• Minor classes
• Monoplacophora
• Solenogastres
• Caudofoveata

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Generalized Mollusc Anatomy
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Gastropod Feeding Apparatus
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Respiration Gills
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Shell Structure Formation
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A Pearl Among the Swine
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Mollusc Reproduction Development

• Indirect development
• Larval stages
• Trochophore larva
• Free swimming, ciliated, shell formation begins
• Veliger larva
• Free swimming, ciliated velium forms,
• Shell/body torsion occurs
• Spat
• Metamorphic form between veliger and juvenile
• Shell elaborates

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Trochophore Larva
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Gastropod Veliger Larva
Mouth
Velia
Shell
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(No Transcript)
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Veliger
Zygote
Trochophore
Juvenile
Spat
Adult
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Adult Abalone
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Class Polyplacophora - chitons
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Polyplacophoran Anatomy
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Class Gastropoda

• The Shell Game

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Class Gastropoda - Torsion
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Gastropod Shell Coiling
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Gastropod Gill/Mantle Cavity Evolution
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Generalized Gastropod Anatomy
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Marine Gastropods
Cowries
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Marine Gastropods
Sea Hare Aplysia sp
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Marine Gastropods - Nudibranch
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Terrestrial Gastropods - Pulmonata

• The mantle cavity serves as a lung
• Glandular epidermis
• Secrete mucus (slime) upon which gastropod glides

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Terrestrial Gastropod - Pulmonata
Pneumostome

• Slugs lack shells
• Mantle thickened
• Pneumostome
• Air intake into mantle cavity

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Phylum Mollusca, Class Bilvalia

• Two shells
• Incurrent excurrent siphons
• No cephalization

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Generalized Bivalve Anatomy
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Generalized Bivalve Anatomy (XS)
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Bivalve Anatomy (Sagittal)
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Bivalves are Typically Filter Feeders
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Bivalve Life Cycle
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Glochidia Unique Larval Stage of Freshwater
Bivalves

• Internal fertilization
• Early development in brood chamber (region of
  mantle cavity)
• Release of glochidia veliger larvae
• Glochidia attach to gills of fish and are
  distributed

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Phylum Mollusca, Class Cephalopoda

• Closed circulatory system
• Shell lost in Octopus, extremely reduced and
  enclosed in mantle in squid, planar spiral in
  Nautilus
• Cephalization
• eye
• Beak around mouth
• Tentacles/arms

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Cephalopod Anatomy
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Squid are the largest Cephalopods
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Nautilus Anatomy
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Cephalopod Eye
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Mating
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Direct Development in Cephalopods
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Color Morphology Changes for Camouflage