Revision of the Recent Polyplacorphora of the Netherlands Investigations by the author have demonstrated that the Dutch Polyplacophora consist of five species of which only two are autochthonous: Leptochiton asellus (Gmelin, 1791) and Lepidochitona cinerea (Linnaeus, 1767). The three others are adventitious: Ischnochiton (Stenosemus) albus (Linnaeus, 1767), Acanthochitona fascicularis (Linnaeus, 1767) and Acanthochitona crinita (Pennant, 1777). Leptochiton cancellatus (Sowerby, 1840) and Tonicella marmorea (Fabricius, 1780) are to be removed from the Dutch list. The only autochthonous record of I. albus from Zwarte Polder (Zeeuwsch-Vlaanderen), proved to be based on a white specimen of L. cinerea. The changing distribution of L. cinerea in the Netherlands is depicted in figs. 6-7. The constantly changing pattern of this common species in the southwestern parts of the Netherlands (fig. 6: triangles — the species is extinct here; squares — the species cannot survive here in the future) is caused by the so-called ‘Delta Plan’, a large scale system of construction of dikes, reclamation of land and establishment of freshwater lakes in an overall attempt to improve the protection against direct influence of the sea.