Body whorl and aperture proportions decline with growth. All from population with deep shell sutures and tumid whorls from mouth of Dee Estuary, Cheshire, England. Aug. 2011.
1 to 3: males (have penes).
4 to 6: females or immature (lack penes).7 to 11: juveniles.
Body whorl decreases from 66% of juvenile 2 mm high shell to 51% of adult 6 mm high.
Aperture decreases from 55% of 2 mm high juvenile to 42% of 6 mm high adult.