FREE-LYING DOMAL BRYOZOAN COLONIES OF THE CASTLE HAYNE LIMESTONE, EASTERN NORTH CAROLINA

Dome-shaped cheilostome bryozoan colonies, approximately 2 cm in diameter, are common among the abundant and diverse bryozoans in offshore deposits of the upper Castle Hayne Formation, southeastern North Carolina. The domes originate in three very different ways: individual colonies of Smittina collum Canu and Bassler; individual colonies of ?Osthimosia sp.; or diverse multispecies overgrowths. The bryozoans typically begin development on a small skeletal fragment and grow laterally beyond this initial substratum without further attachment. All appear to have a larval origin; none are due to regeneration from fragments. Colonies of S. collum typically have heights equal to half their diameters and gently concave undersurfaces. They grow by local eruptive budding, forming subcolonies which extend radially over the underlying layer of zooids. The undersides of subcolonies that extend beyond the original substratum have basal exterior walls that are more commonly fouled by encrusters than is the upper side of the colony. By contrast, the height of ?Osthimosia sp. colonies typically is about two-thirds the diameter, and undersides are gently convex. Lateral growth of these colonies is limited by the size of the original substratum, subcolonies are lacking, and colony growth occurs by prolific frontal budding over the entire upper surface of the colony, The undersides of colonies beyond the substratum consist of the lateral interior walls of marginal zooids and are much less commonly fouled than in S. collum. Multispecies domes are more variable in height:diameter ratio and are less circular in outline. Their upper surfaces by definition are always fouled, and are their undersurfaces are also commonly fouled. Although our specimens have all been collected from quarry spoil piles, their absence from quarries in nearshore facies and their erratic but locally abundant distribution across the spoil suggests that they were patchily distributed and likely limited to particular offshore environments. Free-lying colony-forms are relatively uncommon among post-Paleozoic bryozoans, in contrast to their abundance in the Paleozoic.