Article: Skeletal structure, development and elemental composition of the Ordovician trepostome bryozoan Peronopora

ED spectroscopy of Ca and other elemental densities indicate differences in the rates of secretion and growth among crystallite infrastructures, acanthostyles, the median lamina, zooecial wall, and stages of ontogeny and astogeny in Peronopora. Growth rate (inversely proportional to Ca density) was highest within the granular skeleton of the median lamina and 'A-type' acanthostyles (paurostyles). Growth rate decreased exponentially from the median lamina through the recumbent zone, endozone, and exozone. Paurostyle cores were deposited more rapidly than endozonal wall but less rapidly than recumbent zone wall and the median lamina. Zones of disordered irregular crystallites and laminar growth alternate in zooecial wall axes, and were respectively linked with increased secretion rates and increased episodicity during the cystiphragm/mesozooecial tabulae emplacement cycle. Cu and Mn densities support the sequence of relative growth rates inferred from the Ca data. Paurostyles and the median lamina contain more Cu than other structures. Mn is also most abundant in the median lamina and declined monotonically with reduced growth rate. The median lamina is structurally continuous with the basal lamina but was not secreted against cuticle. Formation of the median lamina and paurostyle cores may be explained by differentiation of inner epithelium for high rates of secretion.