Mercuria similis is a species of small freshwater snail with an operculum, an aquatic gastropod mollusk in the family Hydrobiidae.[1]
This species only tolerates very low salinities, and is perhaps better characterized as a freshwater snail.
The 3–4 mm. high shell is fragile and translucent yellow-white in colour (but often coated with dark deposits). The animal is entirely and uniformly pale and has pale tentacles. Mercuria similis has a proportionately larger body whorl than other hydrobiids.[citation needed]
The shell is short-conical and 3.90–4.50 mm high (Vic-la-Gardiole, Hérault), with a large oval aperture. The penis is long and slim, acute at its distal end, the penial appendix is broad and shorter than the penis which lies on the appendix.[citation needed]