Archaeogastropoda

Archaeogastropoda (also known as Aspidobranchia) was a taxonomic order of snails used in older classifications of gastropods, i.e. snails and slugs. Archeogastropoda are primarily marine prosobranch gastropod mollusks, mainly herbivores, typically having two gills and a double-chambered heart, with the eggs and sperm discharged directly into the water, excepting terrestrial species. They were traditionally regarded as a relatively primitive group.

This older classification of the gastropods is based on the classification of Johannes Thiele (1925). This classification was not based on true phylogenetic relationships, but on more general affinities between the groups. In the last few years, two new cladistic taxonomies of the gastropods have been published (in 1997 and 2005). This has led to an extensive reclassification of gastropod taxa. The taxon Archaeogastropoda was found to be a paraphyletic group, and therefore unacceptable in a strictly cladistic classification.