2001 50 p., 12 figs, 5 col. pls, disbound (no covers). Published in: Zoologische Mededelingen, Leiden.
2001-2018 50, 52, 38, 48 p., 12, 22, 11, 17 figures, 5, 8, 5, 6 coloured plates, disbound (no covers). Published in: Zoologische Mededelingen, Leiden & Archiv für Molluskenkunde. Last part writen with Kathe R. Jensen.
2012 129 p., 29 figs, 79 col. photographs, paperbound. ZooKeys Special Issue.Seventy species of opisthobranchs are described in this work based on collections from the Persian Gulf, Socotra, Kenya, Zanzibar, Madagascar, La Réunion, Mauritius, the Seychelles, the Maldives, and Sri Lanka