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

water

tissue

Hexose & other protein

Collagen

Other

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 hrs

Release 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