REEF DWELLING PARACRINOID WELLEROCYSTIS IN THE LATE ORDOVICIAN KIMMSWICK LIMESTONE, SOUTHEAST MISSOURI

Patch reefs in shallow shoaling paleoenvironments have been reported for the Kimmswick Limestone (Late Ordovician, Katian) in southeast Missouri. This setting hosted many stemmed echinoderms, including the paracrinoid Wellerocystis, which was an abundant endemic form. The type series includes three specimens, all of which suffered significant corrosion, and many details of Wellerocystis’ skeletal anatomy remain unavailable. More than 20 additional specimens were collected by Darrough as part of the Kimmswick Patch Reef Project. Wellerocystis thecae are small but robust, universally preserved without appendages in this agitated setting. The new specimens of Wellerocystis all occurred in close proximity to the patch reef boundstones, unlike the more widespread Kimmswick paracrinoid Comarocystites. It is unclear whether Wellerocystis attached to boundstones or to bioclasts in nearby grainstones. The small stem facet suggests a fixed, encrusting, life-mode tethered by a short stem, based on better-known parallels among other paracrinoids. The Kimmswick is nearly pure carbonate in this area, and echinoderms are generally preserved as partly exposed thecae on weathered joint faces showing various states of solution weathering. Unexposed areas of specimens are embedded in dense carbonate grainstone, ruling out much preparation beyond natural exposure. Among the new material are a few specimens with well-preserved thecal surfaces. These show: 1) a peristome surrounded by four oral plates, 2) a valvular periproct of eight elements, 3) small irregular biserial cover plates, 4) fine pustulose plate ornament, and 5) a lumen running between the adoral groove and the underlying theca. This morphology compares closely with other better-known paracrinoids.