Gastropods, also known as snails or slugs, are a large taxonomic class in the phylum Mollusca. The Gastropods include both sea slugs and snails, freshwater slugs and snails, and land slugs and snails. The number of named Gastropod species is only second to the insects. Although it appears that Gastropods crawl on their stomach, as its name comes from the Greek words "stomach-foot", its stomach is actually on the upper side of the body, called the dorsal side. Gastropods get their shell from the surrounding calcium carbonite in their habitat. However, if a gastropod is not able to access enough calcium carbonite, it forms a transparent shell made of conchiolin, which is secreted by its mantle. Torsion, the 180 degree rotation of the mantle, organs, and shell, is present in all gastropods. There are two mechanical stages in torsion, muscular and mutagenetic, when its genetic information is mutated. Because of torsion, gastropods tend to have their organs mostly on the left side of their body, leaving the right side subsceptible to appendage loss. Instead of the the front body parts on the front of the body, gastropods have them at the back of the body, making it easier to retract it in times of danger. In turn, what is usually found at the end of the body is found near the head.
The Genus Turritella is the most abundantly represented Gastropod Genus in The Maryland Miocene Fauna. Representatives of eight species and varieties have been found in the Lower Fossiliferous Zone of the Calvert Formation. Five are varieties of the very variable species, T. Variabilis Conrad. The typical form (Pl. 22, Fig. 2) is confined to the St. Marys Fauna in Maryland. The variety Cumberlandia Conrad (Pl. 22, Fig. 3, 4) is wide-spread in both the Calvert and Choptank Formations. The variety Exaltata Conrad, confined to the Calvert Formation, has a single strong rib near the base of the whorls, and the side above it is concave to the suture. An unnamed variety has flat-sided whorls that lack ornamentation, and another has strongly convex whorls with the ornamentation very feeble. Both these last varieties are confined to the Lower Fossiliferous Horizon Of The Calvert Formation. Perhaps most abundant in this Lower Calvert Horizon and apparently confined to it, is T. Indentata Conrad (Pl. 22, Fig. 1), with flat-sided whorls and deeply indented sutures on the latter part of the shell. There are two strong ribs on the base of the body whorl, the upper one forms the angulation immediately above the sutures and the lower is submerged on the upper whorls of the shell. T. Aequistriata Conrad (Pl. 22, Fig. 7) is confined to the Calvert Formation, but is a relatively rare species. Turritella Plebia (Pl. 22, Fig. 5, 6, 8) is the most abundantly represented species of the genus in the faunas of all three formations. Typically it is a relatively small form with more or less convex whorls that are marked with fine uniform or uniformly alternating spiral ribs. This (Pl. 22, Fig. 6) is the only form found in the St. Marys Formation. There is, however, some variation in the forms found in the Choptank And Calvert faunas. One variety (Pl. 22, Fig. 5) has flat-sided whorls with very uniform, closely set ribbing. Another (Pl. 22, Fig. 8) has somewhat flat-sided whorls with deep sutures. This latter form is the most abundant representative of the species in the Calvert Fauna, but also occurs in the Choptank Formation.
The Ecphora quadricostata is the official Maryland's official State fossil shell.