New onychochilid mollusks from the Middle and Upper Ordovician of Baltica and Laurentia

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