Shell shape variation. All from large permanent muddy salting-pool on upper Dee Estuary, Flintshire. Salinity 29 p.p.t. (variable), replenished at high water spring tides and by fresh water seepage from Phragmites bed. Aug. 2011.
Height and sex from left to right: 6.5 mm fem, 5.5 mm male, 5mm fem, 5.5 mm fem, 4.5 mm male, 4.4 mm male.
Majority in pool had shallow sutures and flattened whorls but 4.4 mm mature males in image have deep sutures and tumid whorls.