Genetic evidence for two species of lug-worm {Arenicola) in South Wales

Field observations suggest that the common lugworm Arenicola manna (L.) has 2 forms on British shores although taxonomists have htherto mostly recognised it only as a single species showing some morphological variation. Using gel electrophoresis of enzyme systems in homogenised tissue from specimens collected around Swansea (South Wales, UK), we have shown that the 2 forms do not appear to share the same gene pool. The 2 forms are fixed for different alleles at 3 loci out of the 6 which proved to be consistently resolvable and show little similarity in the 2 variable loci at which alleles are shared. Only 4 alleles were found to be common out of 22 investigated. A high value for Nei's Genetic Distance (1.3032) and a low one for Genetic Identity (0.2717) also indicate that they are separate species. An observed heterozygote deficiency is probably due to the mixing of populations as a result of the extended pelagic dispersal phase of larvae and post-larvae.