1. Biology 201 Dr. Edwin DeMont
Molluscan Success
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2. Molluscs
Filmed live
Members of this very diverse group range in size from a few mm to the 18 meter giant squid.
Giant squid
A land gastropod
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3. 1. A body composed of a head-foot and visceral mass.
Molluscs
Molluscs are triploblastic and have bilateral symmetry, but they also have 3 unique features.
1. A body composed of a head-foot and visceral mass.
2. A mantle that encloses the visceral mass, secretes the shell (if present), and forms the mantle cavity.
3. A radula, a rasping structure used in feeding is usually present. The radula has been lost in the bivalves.
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4. Class Gastropoda ~ 35,000 species – the most of any molluscan class.
Molluscs
Class Gastropoda ~ 35,000 species – the most of any molluscan class.
Class Bivalvia includes clams, mussels, oysters and scallops, and is the second largest molluscan class (30,000 described species).
Class Cephalopoda, including octopuses, squid, cuttlefish, and the nautilus, contains the most morphologically complex invertebrates, particularly with respect to the nervous system.
MBL
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5. Squid swimming Muscular mantle Water Radial ‘elastic’ fibers
Escape response – refilling powered by radial muscle contraction.
Muscular mantle
Normal swimming – refilling powered by an elastic mechanism.
Water
Radial ‘elastic’ fibers
Radial muscle fibers
Squid also have fins.
Video
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6. Sessile bivalve- like the mussel in lab
Bivalve Anatomy
Bivalves are laterally compressed and covered by two valves, or shell halves. However, the shell is a single structure with a hinge region. A pair of adductor muscles keeps the shell closed.
Muscle antagonism?
Morphology of swimming scallops is specialized – we will study in the laboratory.
Sessile bivalve- like the mussel in lab
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7. Scallops swim with jet propulsion - thought to be an escape response.
Scallop Swimming
Scallops swim with jet propulsion - thought to be an escape response.
Image source
3. Jets formed
1. Muscle contracts
4. Scallop moves forward
2. Mantle velum seals gap
Click on picture for video
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8. Bivalves are typically sedentary filter feeders.
Bivalve Feeding
Bivalves are typically sedentary filter feeders.
Filter feeding is accomplished by the lamellae of the gills. Gills are used in both respiration and feeding.
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9. Filter Feeding
A physical process which involves very small particles moving through a fluid at low velocities.
Video of viscosity
Small
The behaviour of particles in this physical world is different than our world – it is dominated by viscosity (the ‘stickness of a fluid’).
Large
Small particles in water moving at low velocity ‘see’ a very viscous world.
Click on photos for video
Large particles in water moving at high velocity ‘see’ a very inertial world.
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10. Reynolds number
The type of physical world an object in a fluid experiences can be described by the Reynolds number:
Inertia forces Viscous forces
High Re = whale → inertia → keeps moving.
Low Re = sperm → viscosity → stops immediately.
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11. Reynolds number
Two very different types of flow exist in fluids, and the type of flow depends on the Reynolds number:
Laminar flow
Turbulent flow
Click on photo for video
Nature of interactions of the object moving through the fluid is different depending on what type of flow exists.
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12. Dark arrows – motion after filtering
Bivalve Feeding
Cilia move water into the mantle cavity through the incurrent aperture and it exits through the excurrent aperture.
Collected food is directed to the cilia-covered labial palp surrounding the mouth. The labial palps sort the food and then direct it into the stomach.
Dark arrows – motion after filtering
Video
by Ward and colleagues
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13. On Growth Cones exhibit isometric growth
Other animals exhibit allometric growth.
Animals add more material at the free edge and ‘grow’.
What about growth in other animals?
Exoskeletons?
Endoskeletons?
From: Vogel, S. (2003) Comparative Biomechanics: Life’s Physical World. Princeton University Press.
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