1. Plymouth Marine Laboratory, Citadel Hill, Plymouth PL1 2PB, UK
2. Department of Fisheries and Marine Biology, University of Bergen, Bergen High Technology Centre, N-5020 Bergen, Norway
3. Marine Botany Section, Department of Biology, University of Oslo, PO Box 1069, Blindern, N-0316 Oslo, Norway
4. Electron Microscopy Centre, University of Plymouth, Drake Circus, Plymouth PL4 1AA, UK