1. Hydrobia ulvae. Height in mm and sex, top left to bottom right : 6.5 f, 5.5 m, 5 f, 5.5 f, 4.5 m, 4.4 m. Upper Dee Estuary, salinity 29 p.p.t. Majority; shallow sutures and flattened whorls. A few (2 bottom right); deep sutures & small but adult.
  2. Hydrobia ulvae. Height in mm and sex, top left to bottom right : 6.5 f, 5.5 m, 5 f, 5.5 f, 4.5 m, 4.4 m. Upper Dee Estuary, salinity 29 p.p.t. Majority; shallow sutures and flattened whorls. A few (2 bottom right); deep sutures & small but adult.

Hydrobia ulvae. Height in mm and sex, top left to bottom right : 6.5 f, 5.5 m, 5 f, 5.5 f, 4.5 m, 4.4 m. Upper Dee Estuary, salinity 29 p.p.t. Majority; shallow sutures and flattened whorls. A few (2 bottom right); deep sutures & small but adult.

Submitted by Ian Smith on
Species
Hydrobia ulvae
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I.F. Smith
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All from large 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 on landward side. The great majority of specimens collected had shallow sutures and flattened whorls. A few, like the two at bottom right had deep shell sutures and rounded whorls and were small, though adult.