As implied by its vernacular name, the Grass Cerith, Bittiolum varium (Pfeiffer, 1840), lives in seagrass beds. The Grass Cerith is one of the most common species of mollusks in that particular type of ecosystem, where it supposedly grazes on the microalgae that grow on the seagrass blades. Its shell is small, rarely reaching beyond 4 mm (about 0.16 inch). The shell sculpture shows spiral lines and weak axial ribs that intersect forming raised nodules. The last whorl usually has one or two thickened areas called varices. The shell color is extremely variable, usually light-to dark-brown, sometimes with darker mottlings or specklings. The species occurs in broad area of the western Atlantic and is very common locally.
The Grass Cerith, Bittiolum varium, from Sanibel. Photo by José H. Leal.