Orthothecida
Extinct order of shelled animals / From Wikipedia, the free encyclopedia
The orthothecids are one of the two hyolith orders.[2]
Quick Facts Scientific classification, Families ...
Orthothecida | |
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Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Class: | †Hyolitha |
Order: | †Orthothecida Marek, 1966 |
Families | |
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Marek diagnoses the order thus: Conchs with a flat or concave ventral surface — opercula with large, flat cardinal processes but without clavicles – tightly sigmoidal, sediment-filled intestine – helens absent.
Sometimes the Circothecidae and Tetrathecidae are split out into a separate order 'Circothecida', which is defined by the bottom surface not being flat, the cardinal processes being pronounced, and a circular rim sometimes showing hints of differentiation into clavicles.[3]