Gastropods: Devonian Univalves
Gastropods are a class of shelled invertebrate mollusks that play an important role in the marine and terrestrial fossil record. Their name comes from the Greek word gastro meaning stomach and the Greek word pod meaning foot. This is because their locomotion appears to take place on their belly. The most common forms of modern gastropods are the snails and the slugs, which are closely related to the cephalopods (head-foot).
In the strata bracketing the Alamo Impact Breccia, snail forms are commonly found but not often easy to identify. This is largely due to the fact that all mollusks make their shells from the mineral aragonite, which is unstable at normal surface conditions and is readily subject to diagenesis. As a result, organisms that make their skeletons from calcite (a more stable form of calcium carbonate) are typically more abundant in the marine fossil record, although gastropod steinkerns can be quite common. The only gastropod so far described from the Guilmette Formation is the genus Orecopia.This being said, the abundance and diversity of steinkern morphologies suggests a rich fauna existed on Devonian Period seafloors of present day Nevada.