Shells of the littorinid gastropod Lacuna parva were compared from 23 European localities and postglacial deposits in Sweden. The shells from the recent and the postglacial populations are similar with the exception of the recent population from Ellekilde Hage, Øresund, Denmark. Shells from Ellekilde Hage are different in having especially well developed whorls and only one colour morph. Differences in life-cycle and radula morphometrics further distinguish the Ellekilde Hage population from

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... ulations from the Isle of Wight, UK, and Roscoff, France. No striking differences in penial morphology were observed between the populations. It is suggested that low salinity and subtidal occurrence might be the causative agents of the conchological differences exhibited by the Øresund population. Results Shell morphology The shell of L. parva is approximately 5-6 mm in reproducing females, which are almost twice as large as the males. The shell is very variable, but is generally delicate with three rapidly expanding tumid whorls and deep sutures between them (Fig. 2) . The spire is low with a 150 Fig. 1 Map illustrating the localities along the European coast from which shells of Lacuna parva were collected. Some locality abbreviations identify a group of localities in close proximity: