Abstract
AbstractA new sinistrally coiled univalved molluskCatalanispiran. gen. is described with two species;Catalanispira reinwaldti(Öpik, 1930) from the Middle Ordovician Kõgekallas Formation (Darriwilian) of Estonia andCatalanispira plattevillensisn. gen. n. sp. from the Upper Ordovician Platteville Formation (Sandbian) of northern Illinois, USA. Morphological features include a large, low-trochiform shell, a narrow lenticular aperture, a deep funnel-like umbilicus, a falcate inner lip and a large (1.4 mm wide) protoconch. Ornamentation consists of fine commarginal growth lines or ribs but superimposed on a slightly irregular shell surface.Catalanispiran. gen. is placed within the sinistrally coiled order Mimospirida and the family Onychochilidae, and Catalanispirinae n. subfam. is proposed. The large Lower Ordovician (Tremadocian)PelecyogyraEbbestad and Lefebvre, 2015 from Morocco and France is transferred to this new subfamily. The well-preserved initial growth stage ofCatalanispira plattevillensisn. gen. n. sp. is cap-shaped, slightly asymmetrical, unusually large, and smooth, and represents either an unusually large embryonic shell (protoconch 1) or a larval shell (protoconch 2). It differs from the smaller protoconch described for the clisospirineMimospiraKoken in Koken and Perner, 1925, which might include a multiwhorled larval shell (protoconch 2). Mimospirids are dominantly Ordovician, and have been classified as untorted mollusks (only distantly related to gastropods), dextral hyperstrophic gastropods, or sinistral orthostrophic gastropods. Sinistral asymmetry already in the embryonic shell and lack of conclusive evidence for coiling direction, e.g., an operculum, could suggest thatCatalanispiran. gen. or similar mimosprids were sinistral orthostrophic gastropods. Currently the group is therefore classified as a group of sinistral orthostrophic gastropods, unranked within the Gastropoda.UUID:http://zoobank.org/affc8dcf-4c0f-493d-bee5-75a457996e84
Highlights
Gastropods or gastropod-like mollusks with a sinistrally coiled shell are a small but conspicuous part of Ordovician benthic associations
Abstract.—A new sinistrally coiled univalved mollusk Catalanispira n. gen. is described with two species; Catalanispira reinwaldti (Öpik, 1930) from the Middle Ordovician Kõgekallas Formation (Darriwilian) of Estonia and Catalanispira plattevillensis n. gen. n. sp. from the Upper Ordovician Platteville Formation (Sandbian) of northern Illinois, USA
The group is classified as a group of sinistral orthostrophic gastropods, unranked within the Gastropoda
Summary
Gastropods or gastropod-like mollusks with a sinistrally coiled (left-handed) shell are a small but conspicuous part of Ordovician benthic associations. Most are considered gastropods, defined as mollusks distinguished by the early developmental process of torsion in which all organs of the mantle cavity are twisted (torted) through 180° relative to the head and foot of the animal. The morphologically right side (originally posterior) becomes the topographically left side (and vice versa) when viewed from above, and the mantle cavity lies in an anterior position over the head. Torsion is counterclockwise, which leaves the organs originally on the morphological right side largely intact, forming an anatomically dextral animal
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