1. Microbiology Group, PABIO, University of Wales College of Cardiff, PO Box 915, Cardiff CF1 3TL, UK
2. Anatomy Unit, MOMED, University of Wales College of Cardiff, PO Box 915, Cardiff CF1 3TL, UK
3. Institute of Freshwater Ecology, Windermere Laboratory, The Ferry House, Ambleside, Cumbria LA22 OLP, UK