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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
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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