Hydrostatic skeletons

1
Hydrostatic skeletons
2
The concept

• Fluid volume acting as a skeleton
• Because it is contained
• The material containing the fluid can contract
  against it and change the configuration of the
  container

3
cnidaria

• Two layered
• Ectoderm
• Endoderm
• Basal segments of the cells making up both layers
  have muscle fibers that are at right angles to
  each other

4
Platyhelminthes

• Two fluid containers
• Digestive tract
• Acoelomate, mesoderm is a mesenchyme (parenchyma)
• Muscles
• Circular, longitudinal, and dorso-ventral

5
Nematoda

• Pseudocoelomate-only one layer of mesoderm around
  outside
• Only longitudinal muscles
• Cuticle of fibers in all directions
• Must moult in order to grow.
• Rather inefficient outside of their normal
  environment

6
Another form of pseudocoelomate

• Rotifera
• Muscles for body contraction--inch worm kind of
  pattern of motion
• Cilia wheels on oral surface for both feeding and
  movement