Delicate symmetrical structures in living chambers of autozooecia of some lower Paleozoic species of the order Trepostomata have been interpreted as indications of polypides with little further elaboration. Applications of the anatomy, mode of skeletal growth, and functional requirements basic to living species permit recognition of a few organs of these partially preserved polypides, their functions, and their relationships to enclosing skeletons. Only one basic polypide anatomy is indicated in lower Paleozoic trepostome species, in contrast to the wide diversity of polypide anatomy and their lack of correlation with skeletal characteristics in living stenolaemates. In general, the longer the evolutionary history, the greater the diversity of skeletal morphology in stenolaemates. Apparently, polypide diversity and lack of correlation with skeletal morphology also have increased over time. The complex skeletal septa in autozooecial apertures of the lower Paleozoic trepostome Hallopora have been interpreted as reflecting an organ of full-sized feeding polypides. Applications of the basic biological concepts of living species suggest that the septa provided reduced skeletal apertures to fit smaller polypides of polymorphs that secondarily occupied the living chambers of full-sized degenerated feeding polypides.