|The geographical distribution of the isopods Asellus aquaticus (L.) and A. meridianus Rac.|In: Proceedings of the Zoological Society of London. Academic Press: London. ISSN 0370-2774, more
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Whilst both Asellus aquaticus and A. meridianus may be present in freshwater localities in western Europe, similar localities in the same region may contain only one, or other, or neither of these species. Hitherto no complete explanation of this pattern of local distribution has been presented, although several suggestions have been advanced. In this paper the geographical distribution of the two species is discussed, and an explanation of the local distribution put forward. It is suggested that A. meridianus is the older of the two species in western Europe, and that A. aquaticus is a post-glacial immigrant which is still spreading and replacing A. meridianus.