ZOO 115 Invertebrate Zoology

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ZOO 115 Invertebrate Zoology

• Mollusca

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Mollusca Classes

• Monoplacophora
• Aplacophora
• Polyplacophora
• Gastropoda
• Bivalvia
• Scaphopoda
• Cephalopoda

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Mollusca Class Monoplacophora

• Resemble the generalized mollusc
• Small (3 mm), flattened molluscs that inhabit
  deep water
• Present in the Cambrian period thought to be
  extinct until 1952
• Single shell

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Mollusca Class Aplacophora
www.manandmollusc.net/advanced_introduction/aplac.
html

• 300 species
• Small benthic dwellers between 200-7000m
• Shell-less
• Secrete calcareous spicules on epidermis
• Foot reduced or absent
• No eyes, tentacles, statocysts, or nephridia

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Mollusca Class Polyplacophora

• 800 sp
• Ancient (since late Cambrian)
• Lives in rocky-intertidal region
• Has series of plates for a shell.
• It is an herbivore (except for one species)

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Mollusca Class Polyplacophora
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Mollusca Class Gastropoda

• Marine and terrestrial
• 2nd largest class in animal kingdom
• Hard shell (most)

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Mollusca Class Gastropoda variety
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Mollusca - Class Gastropoda

• Herbivores and predators.
• Has a radula
• Hard shell (most)
• Well developed head and cephalic tentacles
• Locomotion peristalsis of foot.

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Mollusca Class Gastropoda Anatomy
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Mollusca Class Gastropoda - foot

• Columellar muscle
• Retracts head and foot into shell
• Extends head and foot
• Twists foot
• Tarsos muscle
• Bottom of foot and edges
• Locomotion
• Prey capture
• Molding of eggs

• No fluid filled hemocoel

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Mollusca Class Gastropoda Shell Coiling
Planospiral
Whorl
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Torsion

• 180? counterclockwise rotation of visceral mass

WHY?
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Torsion - WHY?

• Larval theory allows foot to be brought up into
  shell

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Torsion - WHY?

• Adult theory
• allows for better ventilation of mantle cavity
  and gills
• Places osphridium anteriorly
• May help increase efficiency of creeping with a
  coiled shell

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Problem from torsion

• Sanitation
• Slits or holes to accommodate waste
• Unidirectional flow of water

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Class Gastropoda - Diversity

• Subclass Prosobranchia
• Order Archeogastropoda
• Order Mesogastropoda
• Order Neogastropoda
• Subclass Ophistobranchia
• Subclass Pulmonata

Molecular evidence indicates that these
classifications are no longer valid!
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Subclass Prosobranchia -

• Usually with a spirally coiled shell (whorl)
• Mantle cavity anterior
• Osphridium (not shown)
• Gills
• Anus
• Nephridiopore (not shown)

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Order Archeogastropoda

• Primative
• Herbivores
• Radula has numerous teeth in transverse rows
• 1-2 bipectinate gills
• Mantle cavity without siphon
• Sexes separate

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Order Archeogastropoda

• Abalone
• Keyhole limpets
• Limpets

Order Patellogastropoda
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Order Mesogastropoda
http//www.seashell-collector.com/beginners/FICIDA
E.jpg
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Order Mesogastropoda

• Operculum present
• Radula with seven teeth/row
• Only left gill unipectinate
• One atrium
• One nephridium

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Order Neogastropoda
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Order Neogastropoda

• Entirely marine
• Radula with 3 or fewer teeth per row
• One gill
• One atrium
• One nephridim

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Order Neogastropoda
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Mollusca Order Neogastropoda Cone snail