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 Muscles 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