Orthogastropoda was a major taxonomic grouping of snails and slugs, an extremely large subclass within the huge class Gastropoda according to the older taxonomy of the ...
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Gastropoda (Ponder & Lindberg, 1997).
This taxon is no longer used according to the taxonomy of the Gastropoda by Bouchet & Rocroi, 2005.
Ponder and Lindberg (1997) in the book The Southern Synthesis, showed the Orthogastropoda as one of two subclasses of the Gastropoda, the other subclass being a very much smaller group called the Eogastropoda, which contained only 5 families of true limpets.
This subclass, Orthogastropoda, which one perhaps could call the true snails, was defined most concisely as all gastropods which were not members of Patellogastropoda, the true limpets.