Shell background colour is green, a really unusual one, but shells getting either white spots and dark irregular small trails are fairly common. These different colouring patterns were the reason for several variety names as: albescens, matoniana, lineata, albomaculata, pallidula etc. of no taxonomic value. Even the form is rather variable. We can find either stretched forms (producta variety) or more roundish ones as compared to the typical form. Typical half-moon form aperture. The thin denticulation in the middle part of columellae lamina is absent in juvenile shells. The average measures reach 6 mm.

Smaragdia viridis (Linnaeus, 1758) Emerald Nerite
Distribution: Southeast Florida, Texas; West Indies; Bermuda. Size: 6 mm to 8 mm.
Description: Color bright emerald green with white mottlings typically outlined in purplish-black; shell solid, subglobular; sculpture glossy smooth; aperture half-moon shaped with 7 to 9 teeth on the inner edge; outer edge thin and sharp; columella flat; operculum green, calcareous with a peglike apophysis just inside the inner edge. Habitat: Typically in seagrass; intertidal to a depth of 20 m (66 ft). Remarks: Collected in Texas from Port Aransas and southward. True S. viridis comes from the Mediterranean, and some workers separate this form into S. viridimaris.
Habitat: Widespread in brackish-water intertidal grass flats.

Atlantic (East and West) and Mediterranean area.

The species feeding activity was studied on a meadow of Zostera marina located in the South of Spain to find it prefers to feed on tenderer tissues of young leaves most during Summer period, an adult specimen devouring up to more than 40 mm2 of vegetable surface tissues.