Transcript Hydrostatic skeletons - Plymouth State University

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