In their work, which has become a standard reference in the field, Ponder and Lindberg (1997) showed that the Orthogastropoda is one of two subclasses of the Gastropoda the class of molluscs, the other subclass being the Eogastropoda.

This subclass, which one could call the true snails, is defined most briefly as all those gastropods which are not members of Patellogastropoda, the true limpets, or its ancestors. They form a monophyletic clade, supported by unambiguous synapomorphies. These synapomorphies (a series of characteristics that appear in its members but not in the other forms it diverged from) are the identifying characteristics of the clade.

Some of the characterisitics are:

• eyes with a vitreous body on eyestalks.
• paired jaws, with their position free from the buccal mass
• a single kidney on the right side of pericardium
• a flexoglossate radula (with a flexible radular membrane). The radula is the snail's tongue, used as a rasping tool.
• unpaired osphradium (olfactory organ).
• lateral ciliated zones of osphradium
• a single left hypobranchial gland (on organ at gill, which releases secretions, such as the reddish dye Tyrian purple).
• an unpaired ctenidium (a comblike respiratory structure in certain mollusks)

Taxonomy

This taxonomy is still under revision.

Superorder Cocculiniformia Haszprunar, 1987

Superorder "Hot Vent Taxa" Ponder & Lindberg, 1997 (systematic position still uncertain)

• Order Neomphaloida Sitnikova & Starobogatov, 1983

Superorder Vetigastropoda Salvini-Plawen, 1989 (limpets)

Superorder Neritaemorphi Koken, 1896

• Order Neritopsina Cox & Knight, 1960

Superorder Caenogastropoda Cox, 1960

• Order Architaenioglossa Haller, 1890
• Order Sorbeoconcha Ponder & Lindberg, 1997
  • Suborder Discopoda P. Fischer, 1884
  • Suborder Murchisoniina Cox & Knight, 1960
  • Suborder Hypsogastropoda Ponder & Lindberg, 1997

Superorder Heterobranchia J.E. Gray, 1840

• Order Heterostropha P. Fischer, 1885
• Order Opisthobranchia Milne-Edwards, 1848
  • Suborder Cephalaspidea P. Fischer, 1883
  • Suborder Sacoglossa Von Ihering, 1876
  • Suborder Anaspidea P. Fischer, 1883 (sea hares)
  • Suborder Notaspidea P. Fischer, 1883
  • Suborder Thecosomata Blainville, 1824 (sea butterflies)
  • Suborder Gymnosomata Blainville, 1824 (sea angels)
• Order (not yet named)
  • Suborder Nudibranchia Blainville, 1814 (nudibranchs)
• Order Pulmonata Cuvier in Blainville, 1814 (pulmonates)
  • Suborder Systellommatophora Pilsbry, 1948
  • Suborder Basommatophora Keferstein in Bronn, 1864 (freshwater pulmonates, pond snails)
  • Suborder Eupulmonata Haszprunar & Huber, 1990

References

• Gastropods on Land by G.M. Barker. Chapter 1 available online in PDF format here
• Orthogastropoda taxonomy at NCBI

Gastropods

Orthogastropoda