1Laboratory of Anatomy, URA 1137, Museum d'Histoire Naturelle, F-75005 Paris, France
2Hautes Ecoles Provinciales du Hainaut Occidental & Centre Agronomique de Recherches Appliquée du Hainaut, rue Paul Pastur 11, B-7800 Ath, Belgium
3Department of Zoology & Animal Ecology, University College Cork, Lee Maltings, Prospect Row, Cork, Ireland
4University Marine Biological Station Millport, Isle of Cumbrae KA28 0EG, Scotland