openings
A
echinoderms
Castes
Echinoderms are invertebrates with an internal skeleton and a system of fluid-filled tubes called water vascular system.
Echinoderms are invertebrates with an internal skeleton and a system of fluid-filled tubes called a water vascular system. There are four major groups of echinoderms: sea stars, brittle stars, sea urchins, and sea cucumbers.
Vacuoles
The fluid filled spaces in the brain are called ventricles. The fluid is called cerebrospinal fluid
fluid filled sapce within the cytoplasm: temporarily stores food
Bursa or Bursae
fluid-filled cavity formed within the mesoderm of some animals
The ventricles are fluid filled cavities of the brain.
Echinoderms also have a spacious coelom (an open, fluid-filled body cavity lined with tissue), large gonads, and (usually) a complete gut.