BUILDING BIGGER AND BETTER ANIMALS SUPPORT AND LOCOMOTION

Pandorina Pleodorina Eudorina Gonium 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 (SO 2 )]Calcareous [Calcium (CaCO 3 )] 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

Composition of anemone body 92% 8% 85% 9%6%

Behaviour of collagen Stress test - mesoglea 300% original length Stretch for hrs Release load Stress test - collagen 102% of original length Stretch for 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 (%) NormalIf cross-linked % 30%

Why aren’t they cross-linked? +/- 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 J.Exp.Biol.205: 427 Prolate Oblate

Jellyfish Shapes ProlateOblate

Jellyfish Shapes Collin & Costello J.Exp.Biol.205: 427 h d

Jellyfish Shapes Fineness ProlateOblate

Swimming of Prolate and Oblate Jellyfish ProlateOblate 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 muscle fluid

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