Muscle scars, shell form and torsion in Cambrian and Ordovician univalved molluscs

摘要: Runnegar, Bruce 1981 12 15: Muscle scars, shell form and torsion in Cambrian Ordovician univalved molluscs. Lethaia, Vol. 14, pp. 311–322. Oslo. ISSN 0024–1164. Well preserved muscle scars have been discovered on one or more specimens of the early Palaeozoic molluscs Pelagiella, Matherella, Sinuites ?Bucania. From this information it is argued that bellerophonts ?Bucania were untorted, Pelagiella had undergone about 10° torsion, Matherella may a fully torted, hyperstrophic descendant Pelagiella. Other gastropods such as Aldanella could independently derived from therefore Class Gastropoda be at least diphyletic. In general, small dextrally coiled archaeogastropods pelagiellids are most common asymmetrical univalves Early Cambrian, but rare ultradextral (hyperstrophic) forms also known. Only known Middle dominate Late Cambrian. As result, slit-bearing not before Ordovician. Yuwenia bentleyi gen. et sp. nov. new taxon proposed work. *Mollusca, Gastropoda, Monoplacophora, anatomy, evolution, Ordovician, n.g.