Abstract
Histological analysis revealed three types of mucous cells present in the tissues of Pteraster tesselatus Ives. They were all unicellular in structure and each was restricted to certain areas of the anatomy. Mucus produced by these gland cells was forced out onto the aboral surface of Pteraster by water pressure generated within the nidamental cavity (respiratory chamber). Water flow in and out of the respiratory chamber was powered both by muscle contractions and a complex network of overlapping ossicles. Ambient sea water was allowed into the respiratory chamber only through large pores lining the ambulacral groove. Expulsion of respiratory water out of the chamber was by either one of two different pathways. In defence, water and secreted mucus were forced out of the numerous spiracular openings that perforate the supradorsal membrane. When, on the other hand, the sea star was not in a defensive posture, water was simply passed out through the centrally located osculum.
Published Version
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