Quagga Mussel (Dreissena bugensis rostriformis) is similar to the Zebra Mussel (Dreissena polymorpha), it has not been reported in Wales yet but has been found in Wraysbury Reservoir and the Wraysbury River near Egham, Surrey after spreading steadily through Europe towards the UK. Like the Zebra Mussel it can produce severe negative effects on local ecosystems and marine activities.
Please see here for information on identification: https://secure.fera.defra.gov.uk/nonnativespecies/downloadDocument.cfm?id=802
See here for the factsheet on the Quagga Mussel: https://secure.fera.defra.gov.uk/nonnativespecies/factsheet/downloadFactsheet.cfm?speciesId=3831
Please submit any sightings in West Wales with photographs to WWBIC (info@westwalesbiodiversity.org.uk) and to CEH here: http://www.brc.ac.uk/risc/alert.php?species=quagga_mussel