When in water (right), shell is more translucent, lighter and brighter in colour, and less reflective, than when in air (left).
1: internal view of row of palatal protrusions at earlier position of palatal lip.
2: external view through translucent shell of same row of protrusions as in ‘1’.
Shell height 6.1 mm. Salting on tidal River Dee, Flintshire, Wales. December 2018.