Molecular and morphometric variation in European populations of the articulate brachiopod Terebratulina retusa

Molecular and morphometric variation within and between population samples of the articulate brachiopod Terebratulina spp., collected in 1985–1987 from a Norwegian fjord, sea-lochs and coastal sites in western Scotland, the southern English Channel (Brittany) and the western Mediterranean, were measured by the analysis of variation in the lengths of mitochondrial DNA (mtDNA) fragments produced by digestion with nine restriction endonucleases and by multivariate statistical analysis of six selected morphometric parameters. Nucleotide difference within each population sample was high. Nucleotide difference between population samples from the Scottish sites, both those that are tidally contiguous and those that appear to be geographically isolated, were not significantly different from zero. Nucleotide differences between the population samples from Norway, Brittany, Scotland and the western Mediterranean were also very low. Morphometric analysis confirmed the absence of substantial differentiatio