Archaeogastropoda

Archaeogastropoda is an extinct or greatly reduced superorder of marine gastropod mollusks, traditionally classified within the class Gastropoda. The group is notable for its historical significance in the evolutionary development of snails and their relatives, though its taxonomic boundaries have been subject to revision in modern phylogenetics.

Members of Archaeogastropoda are characterized by their coiled shells, often with a distinct operculum—a hard structure used to seal the shell opening when the animal retracts. Fossil records indicate that these mollusks appeared in the Cambrian period, around 500 million years ago, making them among the earliest known gastropods. They thrived throughout the Paleozoic and Mesozoic eras, with diverse forms occupying various marine habitats, including shallow waters and deeper oceanic environments.

Notable fossil genera include *Bellerophon*, known for its distinctive, often asymmetrical shells, and *Maclurites*, which had elongated, spiral-shaped shells. Archaeogastropods played ecological roles similar to modern snails, acting as scavengers and grazers in their ecosystems. Their decline began in the Cretaceous period, coinciding with the rise of more advanced gastropod groups like the Heterobranchia and Patellogastropoda.

Taxonomic classifications have evolved, with some modern studies suggesting that Archaeogastropoda may not represent a monophyletic group. Genetic and morphological analyses have led to the reclassification of certain families into other superorders, such as the Neritimorpha and Trochomorpha. Despite this, the term persists in paleontological and historical contexts to describe early gastropod lineages.

Today, only a few living representatives, such as the genus *Haliotis* (abalone), are sometimes loosely associated with Archaeogastropoda, though they belong to more recently defined clades. The study of Archaeogastropoda remains important for understanding the early diversification of gastropods and the evolutionary transitions that shaped modern marine mollusks.