Aanwijzingen voor geografisch polymorfisme bij de Harlekijnslak Polycera quadrilineata (O.F. Müller, 1776)

Specimens of the Four-striped polycera Polycera quadrilineata (O.F. Müller, 1776) collected in the autumn of 2021 from Thorny sea mat Electra pilosa on the beaches of Wijk aan Zee and Egmond aan Zee (province of North Holland) were observed to differ both in pigmentation and in anatomical traits from specimens regularly encountered in the Eastern Scheldt basin. These differences may be induced by the different biotopes (i.e., be phenotypic) or depend on clustered genetic differences. More extensive research is needed to underpin the preliminary conclusions.