The Archaeogastropoda are likely the oldest Gastropods dating back to the Ordovician, perhaps Cambrian. They still exist today as a sub-class. The protoconch is one-piece with only one whorl. Often the inner layer of the shell is composed of nacre. The aperture is holostome. Most species are herbivor and develop lecitotrophic larva. They are all endogastritic. Radula most commonly rhipidogloss or docogloss.
Unless otherwise noted all examples are of marine origin.
Patellogastropoda
- cup-like shell
- apex points backward
- shell mostly calcitic
- embryonic shell planispiral and sinistral
- main genus
- shell with radial ribs
- suction foot
- U-shaped muscular impression
- no nacre
- habitat/life: sublittoral, grazing, hard substrates, not tropical
- Trias - today
Pleurotomaria
- "slit-band" - and partially open incission into the shell (does anyone know what is the proper english language word for this?)
- nacre
- today: abyssal
- mesozoic: shelf
- ear-like shell
- nacre
- thick muscular impression
- cup-shape secundary, teleconch coiled
- "slit-holes" - holes instead of a "slit-band"
- lower tidal zone, grazing, herbivor
- cooler water
- Cretaceous - today
- grazers, herbivor
- edges
- flat basis
- operculum
- Cretaceous - today
- eats Hydrozoans
- grows concentrically
- calcitic???
- cup-like shell
- no nacre
- porcellane-like shell
- "breathing hole" on top
- tropics
- Trias - today
- beware of confusion with Patella!
- derived from Fissurella?
- appearance similiar to Pleurotomaria
- "slit-band"
- planispiral coiling
- "slit-band"
- thick shell
- no nacre
- Cambrian - Trias
- exogastritic!
- questionable classification! Maybe it's a Monoplacophora?
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