FAMILY: HYDROBIIDAE associated with brackish-water
The shell illustrated here lacks its operculum.
Genus: MERCURIA
The only species found in Britain is Mercuria cf. similis and it is at the edge of its geographical range. It is restricted to almost fresh waters, occurring in upper tidal reaches of quiet running river estuaries and tidal ditches and pools.
Mercuria cf. similis
(Draparnaud, 1805)
Mercuria cf. similis (Draparnaud, 1805)
Description: The shell is small, semitransparent and rather glossy, with a blunt apex. The umbilicus is distinct. The broad squat shell is of 5 – 6 tumid whorls which are flattened below the deep sutures. The body whorl forms about 75% of the height of the shell. The snout is dark with a pale tip. An orange-yellow spot occurs behind each eye. The tentacles bear a central longitudinal brown band.
Size: Height: 4 mm. Breadth: 2 mm.
Habitat: Occurs where the water is brackish but nearly fresh, mainly in the upper tidal reaches of quiet-running rivers, on plants or the muddy edges or bottoms of water channels.
Anderson (2005) makes a good case for leaving the name of this species conditional until further work has been carried out. The species was previously known in Britain and Ireland as Mercuria confusa (Frauenfeld, 1863).