Letteratura scientifica selezionata sul tema "Edrioasteridae"

AbstractThe new edrioasterinePseudedriophus guensburgin. gen. n. sp., is described from the Lower Ordovician Ninemile Shale of central Nevada based on three complete to partial small specimens, a well-preserved large ambulacrum, and an isolated ambulacral floor plate. The weathered-out holotype of this edrioasterine exposes the bottom surface of the theca that bears an aboral collar, peduncular stalk, and attachment disk, features that are poorly known in this clade. These specimens were found with a single specimen of a new edrioblastoid,Porosublastus inexpectusn. gen. n. sp., only the second edrioblastoid ever found in the Early Ordovician. Some of the ambulacral cover plates are stripped off one of the ambulacal grooves, revealing new information about how the ambulacra are built in this rare group of bud-shaped edrioasteroids.

Echinoderms are important faunal components in the Curdsville Member of the Lexington Limestone. Numerous clades are represented, including Crinoidea (Springer, 1911; Parsley, 1981), Paracrinoidea (Parsley and Mintz, 1975; Parsley, 1981), Cyclocystoidea (undescribed), Edrioasteroidea (Miller and Gurley, 1894; Bell, 1976, 1979), and Stylophora (Parsley, 1981, 1991). Although some of these taxa are well preserved (Springer, 1911), most have been recovered from residues of acidized samples. These later specimens are poorly preserved, obscuring much of the information. Here we describe well preserved specimens recently collected by members of the Kentucky Paleontological Society (Lexington) of two species that add significantly to our understanding of lesser known components of the Curdsville Fauna. Bistomiacystis schrantzi n. sp. is a large paracrinoid bearing two separate ambu1acral systems that lead to two peristomial openings. Our research suggests that this unusual arrangement is consistent with oral areas of other derived blastozoans bearing oral plates. Edrioaster priscus (Miller and Gurley) is a poorly known large edrioasterid edrioasteroid previously known only from specimens preserved in coarse beekite. The new material of this taxon allows for a thorough characterization of this poorly known edrioasteroid and shows that previous assessments of its size and morphology need revision.

Although echinoderm debris is locally common, articulated specimens are rare in Late Cambrian rocks from the Great Basin and Rocky Mountains of the western United States and are mostly associated with hardgrounds. The fauna, including cornute stylophorans, trachelocrinid eocrinoids, solute homoiosteleans, and rare edrioasteroids, includes several members of the archaic Cambrian Evolutionary Fauna, which had already passed its maximum diversity for echinoderms. In addition to the low diversity, articulated specimen abundance is very low, averaging only about one-tenth that found in overlying Lower Ordovician units. The transition between the Cambrian and Paleozoic Evolutionary Faunas for echinoderms in North America apparently occurred rapidly very close to the Cambrian-Ordovician boundary, because no unequivocal examples of the Paleozoic fauna (such as crinoids, glyptocystitid rhombiferans, asteroids, or echinoids) were found in the Late Cambrian sections.New taxa include several cothurnocystid stylophorans assigned to Acuticarpus delticus, new genus and species, Acuticarpus? republicensis, new species, and Archaeocothurnus goshutensis, new genus and species; Scotiaecystis? species, a poorly preserved cornute stylophoran with lamellipores; Minervaecystis? species, a fragmentary solute homoiostelean based on several steles; Tatonkacystis codyensis, new genus and species, a well-preserved trachelocrinid eocrinoid with five unbranched arms bearing numerous brachioles; an unnamed, poorly preserved, epispire-bearing eocrinoid; an unnamed, poorly preserved, globular eocrinoid? lacking epispires; and an unnamed, heavily weathered, edrioasterid edrioasteroid. Nearly all holdfasts found in these Upper Cambrian units are single-piece blastozoan types, probably belonging to trachelocrinid and other eocrinoids. Distinctive columnals and thecal plates of several additional undescribed eocrinoids and other echinoderms were locally abundant and are also described.

AbstractRhenopyrgids are rare, turreted edrioasterid edrioasteroids from the lower Paleozoic with a distinctive and apparently conservative morphology. However, new, well-preserved rhenopyrgid edrioasteroid material from Canada, along with a review of described taxa, has revealed broader structural diversity in the oral surface and enabled a re-evaluation of rhenopyrgid functional morphology and paleoecology.The floor plates in Rhenopyrgus viviani n. sp., R. coronaeformis Rievers, 1961 and, R. flos Klug et al., 2008 are well fused to each other and the interradial oral plate and lack obvious sutures, thereby forming a single compound interradial plate. This differs from other rhenopyrgids where sutures are more apparent. Such fused oral surface construction is only otherwise seen in some derived edrioblastoids and in the cyathocystids, suggesting homoplasy.Our analysis further suggests that the suboral constriction could contract but the flexible pyrgate zone could not. Thus, specimens apparently lacking a sub-oral constriction should not necessarily be placed in separate genera within the Rhenopyrgidae. It also supports rhenopyrgids as epifaunal mud-stickers with only the bulbous, textured, entire holdfasts (coriaceous sacs) anchored within the substrate rather than as burrow dwellers or encrusters.Rhenopyrgus viviani n. sp. is described from the Telychian (lower Silurian) Jupiter Formation of Anticosti Island, Québec, Canada and is differentiated by a high degree of morphological variability of pedunculate plates, broader oral plates, and narrower distal ambulacral zones. Specimens lacking or with obscured diagnostic plates from the Ordovician of Montagne Noire, France, and the Ordovician and Silurian of Girvan, Scotland are also described.UUID: http://zoobank.org/7f81d67f-4155-4719-8a45-b278ad70739d