Solenotheca, New Hyolitha (Mollusca) From The Ordovician Of North-America

Volume: 103Start Page: 265End Page: 27

Early Mississippian Hyolitha from northern Iowa

Volume: 33Start Page: 343End Page: 35

New Hyolitha from the Devonian of Bolivia

International audienceNew finds of Hyolitha in the Devonian of Bolivia consist of the hyolithid Bolithes crasquinae new genus and species, which is the first well-preserved hyolithid from strata of this age in the region. In addition, specimens of the orthothecids Bolitheca steinmanni (Knod, 1908) and Neobactrotheca pharetra Marek and Isaacson, 1992 serve to increase knowledge concerning the range of morphologic variability within those taxa. Incompletely preserved hyoliths include Hyolithes sp. indet.? which would be the first definitive representative of that genus from South America. Two polyclaviculate hyolithid opercula, and an unusually large hyolithid conch are left in open nomenclature. The large conch is noteworthy because of signs of failed predation, making this only the second hyolithid on record on which the effects of predation can be recognized, and the first from the Devonian of South America. Hyolithes dorbignyi Kozlowski, 1923 is transferred to 'Hyolithes' owing to poor preservation

Devonian (Givetian) Hyolitha from the Kersadiou formation (Massif Armoricain, France

International audienceAmong hyoliths from the Givetian Kersadiou Formation in northwestern France one form is assigned to Hyolithes triliratus Hall, 1879, which is used as the basis for Brittanella new genus. The occurrence of this species in France supports affinity for fauna in that region to the Eastern Americas Realm. Other hyoliths from this unit include one species of Hyolithes Eichwald, which is left in open nomenclature, and one conch and one platyclaviculate operculum that cannot be identified to genus. The occurrence of these fossils in concretions in an oxygen-stressed dark gray shale supports the notion that this environment served as a refuge for taxa that were less efficient competitors with other normal marine benthos in the Devonian

'Mediterranean Province' hyoliths from the middle Cambrian and Upper Ordovician of Sweden

Nine species of hyoliths are described based on material collected in Skane, southern Sweden, during the first half of the last century. The material derives from the middle Cambrian (Cambrian provisional Series 3) Exsulans Limestone Bed at Almbacken east of Lund and the Upper Ordovician (Katian-Hirnantian) Lindegard Formation at Tommarp west of Simrishamn. The Almbacken assemblage consists of three taxa; Nephrotheca ruderalis Marek, 1989?, Buchavilites sp., and Orthothecid sp. 3. The Tommarp assemblage comprises Bactrotheca deleta Novak, 1891, Circotheca sp., Sololites sp., Orthothecid sp. 1 and 2, and one species of Quadrotheca Sysoev, 1958. Albeit small, the collections, altogether comprising some twenty specimens, have important paleobiogeographic implications for these metazoans. All hyoliths documented herein were formerly regarded as occurring solely in the 'Mediterranean' paleobiogeographic province, encompassing central and southwestern Europe, and North Africa. The material at hand reveals that the distribution of Buchavilites Marek, 1975, Circotheca Sysoev, 1958, Nephrotheca Marek, 1967, Quadrotheca, and Sololites Marek, 1967 is now extended to Baltica, further eroding the assumed strongly provincial nature of these organisms

A Complete Reconstruction of the Hyolithid Skeleton

Hyolithids are a group of Paleozoic lophotrochozoans with a four-pieced skeleton consisting of a conch, an operculum, and a pair of lateral 'spines' named helens. Both the conch and operculum are relatively well known and, to a certain extent, have modern analogues in other lophotrochozoan groups. The helens, on the other hand, are less well known and do not have clear modern analogues. This has hindered the knowledge of the complete morphology of the hyolithid skeleton, as well as other aspects of hyolithid biology, such as the organization of soft parts, and their ability to move. The material studied herein, consisting of disarticulated skeletal elements from the Silurian of Gotland, Sweden, illustrates a complete developmental sequence of a hyolithid species and includes the first complete, three-dimensionally preserved helens. Our material confirms that helens were massive skeletal elements, whose growth started proximally with the deposition of a central, coherent lamella. Further shell accretion took place around this lamella, but followed a particular accretion pattern probably constrained by the presence of marginal muscle attachment sites on the proximal-most portion of the helens. These muscle attachment sites were ideally located to allow a wide range of movements for the helens, suggesting that hyolithids may have been relatively mobile organisms

Palaeobiology of orthothecide hyoliths from the Cambrian Manto Formation of Hebei Province, North China

Newly discovered specimens of the orthothecide hyoliths in Hebei Province of North China reveal new data on diversity, skeletal microstructure and palaeoecology of the order Orthothecida. Decoritheca cyrene possesses a well-defined skeletal structure consisting of rows of tubercles in the shell wall, which correspond to dimples on the internal surface of the conch. We describe a new species Cupitheca convexa sp. nov. characterised by a planar and interior convex operculum with a pair of bilobate cardinal processes, which differs from the more widespread C. holocyclata in opercular morphology and overall ornamentation of the conch, highting the significance of operculum in the classification of hyoliths. First discovery of the presumed unusual protoconch of C. convexa sp. nov. implies a possible lecithotrophic development to adapt to nutrient-fluctuant environments. Pitting structure on the operculum and shell as well as lamellar- fibrillar structure on the internal mould of C. convexa sp. nov. are observed herein

New late Palaeozoic Hyolitha (Mollusca) from Oklahoma and Texas, and their palaeoenvironmental significance

Volume: 29Start Page: 303End Page: 31

New Middle Ordovician hyoliths from the Ossa Morena Zone, southwestern Spain

The record of Middle Ordovician (Oretanian, ca. Darriwilian 2) hyolithids from the Ossa Morena Zone of the Iberian Massif in southwestern Spain is increased with the recognition of Robardetlites sevillanus n. gen. n. sp., Andalucilites parvulus n. gen. n. sp., Pauxillites desolatus n. sp., Leolites malinkyi Marek and Gutiérrez-Marco n. sp., and Cavernolites sp. in that region. Andalucilites n. gen. and Robardetlites n. gen. are endemic whereas the other genera are known from coeval strata in the Barrandian region in central Europe, France, and Morocco, giving this assemblage a decidedly “Mediterranean province” character. The discovery of Pauxillites, Leolites, and Cavernolites in Iberia extends their geographic ranges to that region, and Leolites from this area extends its stratigraphic range downward, making its occurrence in Iberia the oldest known for that genus