1. Centro Nacional de Biotechnología (CNB-CSIC), Campus de la Universidad Autónoma de Madrid, 28049 Madrid, Spain
2. Present address: Centro de Investigaciones Biológicas (CIB-CSIC), 28040 Madrid, Spain.
3. Department of Marine and Environmental Sciences and Department of Biology, Northeastern University, Marine Science Center, Nahant, MA 01908, USA
4. Departamento de Biología Molecular, Universidad de Cantabria-IFIMAV, 39011 Santander, Spain