e D D.1 and D.2: Yochelcionella and Helcionella are small Middle Cambrian monoplacophorans from Australia, ranging in size from about 4 to 7 mm.D.3 and D.4: Dyeria and Lophospira are Ordovician gastropods from Ohio and New York, about 30 mm in size. D.5 and D.7: Fossil and extant cephalopods. D.5: Reconstruction of the curved Upper Silurian genus Glossoceras from Sweden; part of the shell has been cut away to show the chambers and siphuncle, about 25 mm in size. D.6: The coiled Middle Cretaceous ammonite Falciferella from England, about 25mm in size. D.7: The living coiled shelled genus Nautilus from New Caledonia, about 150 mm in size.