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# of Described Species: First Appearance: Habitats: Marine, in the water column Shapes: Planar spiral Feeding Types: Carnivores |
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| The nautiloides include the chambered nautilus and its many fossil relatives. They first appear in the Late Cambrian and underwentgo a rapid diversification in the Ordovician. All have a spiral nacreous shell with interconnected internal chambers. The head is covered with a hood and has numerous short, suckerless tentacles. There are two pairs of gills and, unlike coleoids, there is no ink sac. |