BUILDING BIGGER AND BETTER ANIMALS SUPPORT AND LOCOMOTION
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BUILDING BIGGER AND BETTER ANIMALS
SUPPORT AND LOCOMOTION
Pandorina Pleodorina
EudorinaGonium
Chlamydomonas
Volvox
Beginnings of the Metazoa?
Metazoan Evolution
Two consequences
1) Need for support
2) Need for coordinate locomotory apparatus
Design of the support system
Method of movement
Going to look at
1) Sponges
2) Hydrostatic skeletons – anemones and jellyfish
3) Acoelomates
4) Molluscs
5) Exoskeletons
6) Notochords
Anatomy of an Asconoid Sponge
- spicules embedded in the mesohyl Same principle as putting straw in mud bricks
Sponge structure - Support
Siliceous [Silica (SO2)] Calcareous [Calcium (CaCO3)]
Spongin [Protein]
Arrangement of spicules can be haphazard or very precise
The Cnidarians
Mesoglea
Collagen
Collagen Fibres in Metridium
unstressed angle – 40 – 45º
1) Crossed helices (outer layer)
Collagen Fibres in Metridium
circumferential
radial
watertissue
Hexose & other proteinCollagenOther
Composition of anemone body
92%
8%
85%
9% 6%
Behaviour of collagen
Stress test - mesoglea300% original length
Stretch for 12-15 hrs
Release load
Stress test - collagen 102% of original lengthStretch for
12-15 hrsRelease load
How can mesoglea (85%) collagen stretch to 300% if collagen itself stretches only 2%?
Behaviour of collagen
1) Matrix in which it sits is important
2) Collagen fibres are not joined
How can mesoglea (85%) collagen stretch to 300% if collagen itself stretches only 2%?
Slide past one another
What is in the mesogleal matrix?
High molecular weight polymer- protein / polysaccharide complex
Dilute gel
What is in the mesogleal matrix?
Collagen fibres not directly cross-linked
Extension (%)
Normal If cross-linked
300
150
0
300%
30%
Why aren’t they cross-linked?
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weak cross-links+/- seawater ions
Preserved Anemone
- matrix is cross-linked by formaldehyde
How do they move? – Cnidarian nerve nets
Simplified Scyphozoan Anatomy
Velum
Jellyfish Shapes
Collin & Costello 2002. J.Exp.Biol.205: 427
Prolate
Oblate
Jellyfish Shapes
Prolate Oblate
Jellyfish Shapes
Collin & Costello 2002. J.Exp.Biol.205: 427
h
d
Jellyfish Shapes
Fineness
Prolate Oblate
Swimming of Prolate and Oblate Jellyfish
Prolate Oblate
Opening of bell
Closing of bell
Opening of bell
Closing of bell
Hydrostatic skeleton
For a fluid the change in pressure is equal in all directions
Δp
contracting area
Hydrostatic skeleton
How do you apply pressure?
Either
1) Add fluid to system
2) Move fluid around
musclefluid
A slight diversion – Acoelomates and Molluscs
Nemerteans Platyhelminthes
Molluscs
Direction of wave
Direction of motion
Movement in Aceolomates/Molluscs
1) Direct
Direction of wave
Direction of motion
Movement in Aceolomates/Molluscs
2) Retrograde
points d’appui
4) Ditaxic3) Monotaxic
In the molluscs
Changes in locomotion
Gibbula
Confronts obstacle
Snail has peculiar problem
Remember the standard coelomate body plan.
Step 2 - Put a fold of tissue dorsally
Step 1 - Expand the lower body wall
Step 3 - Put a shell over top
How do you build a mollusc?
Snail has peculiar problem
How do you build a mollusc?
Visceral mass + shell
Foot
Problem of torque (or twisting)
Snail has peculiar problem
How do you build a mollusc?
Problem of torque (or twisting)
Columnar muscles
Extremes of this kind of locomotion
Leeches
Caterpillars
2 points d’appui