Tuesday, May 13, 2008

Gastropoda - Archaeogastropoda

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Today I will try to give a brief overview of the most important members of the Archaeogastropoda. I will discuss shortly the three most important super-orders with examples of important orders or families.

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
Patella
  • main genus
  • shell with radial ribs
  • suction foot
  • U-shaped muscular impression
  • no nacre
  • habitat/life: sublittoral, grazing, hard substrates, not tropical
  • Trias - today
Vetigastropoda

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
Haliotis
  • 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
Trochus
  • grazers, herbivor
  • edges
  • flat basis
  • operculum
Calliostoma
  • Cretaceous - today
  • eats Hydrozoans
Turbo
  • grows concentrically
  • calcitic???
Fissurella
  • cup-like shell
  • no nacre
  • porcellane-like shell
  • "breathing hole" on top
  • tropics
  • Trias - today
  • beware of confusion with Patella!
Scissurella
  • derived from Fissurella?
  • appearance similiar to Pleurotomaria
  • "slit-band"
Bellerophontida
  • planispiral coiling
  • "slit-band"
  • thick shell
  • no nacre
  • Cambrian - Trias
  • exogastritic!
  • questionable classification! Maybe it's a Monoplacophora?

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