Any of the members of the class Gastropoda on Old Earth. This group included many thousands of species of marine snails and sea slugs, as well as freshwater snails and limpets, and the terrestrial snails and slugs.
Gastropods were the most diversified class within the phylum Mollusca, itself a very successful group, and second only to insects in its number of species; 80,000 are believed to have existed before the Great Dying, and over 60,000 of these have been recovered from nodes of the Burning Library project. (GAIA is believed to have reconstructed nearly all of the remainder). The group was quite striking in its habitat diversification, with representatives live in gardens, in woodland, in deserts, and on mountains; in small ditches, great rivers and lakes; in estuaries, mudflats, the rocky intertidal, the sandy subtidal, in the abyssal depths of the oceans, and numerous other ecological niches, including parasitic ones. They are similarly important elements in the fauna of most Terragen-derived ecosystems today, and the number of extant species is very large, especially when one includes non-sophont lazurogens, tweaks, and splices.
As might be expected given the nature of the original set of species, the proportion of gastropod provolves and rianths is small, particularly by contrast with the relatively large numbers of sophont clades derived from their sister class the cephalopods. Nevertheless the Malacologists of New Duibbiyat, gastropod rianths all, have given rise to a number of notable provolve clades, including Cymbium sapiens and the Aruans.