ABSTRACT
Two of the most obvious examples of the use of hydrostatic pressure for skeletal purposes in the Echinodermata lie in the Ho 1othuroidea and in the water vascular systems of all the echinoderm classes. No measurable hydrostatic pressure was to be found within the perivisceral cavity of Asterias rubens when at rest. There are instances however when an increase in pressure is conceivable, such as during spawning or during eversion of the stomach.
