Carel Philip Sluiter (1854-1933) started his acedemic studies at the Athenaeum Illustre (later to become the University of Amsterdam), but finished at the University of Leiden. He got his promotion on a thesis on lamellibranchiate molluscs. In 1878 he was asked to participate in a cruise to the Arctic (Spitsbergen, Novaya Zembla) by the whaling vessel 'Willem Barents', which yielded extensive collections still kept in ZMA (cf. above). Shortly afterwards, he took a job as teacher in Batavia (now Jakarta) for two years, where he was an active researcher on the fauna of the Bay of Batavia, with special interest in reefs, echinoderms and tunicates. In 1891 he returned to Amsterdam, where he became Professor Weber's assistant as teacher in the university. In 1898 he succeeded Weber as Professor of Zoology. When Weber returned with the rich Siboga collections, he was offered (and accepted) to write the monographs on holothuroids, gephyreans, sipunculids, echiurans and ascidians (Ihle, 1933)

Jan Versluys Jzn (1873-1939) studied biology at the University of Amsterdam and graduated in 1895. At that moment he was invited by Count de Dalmas to participate in an expedition to the Caribbean on board the sailing vessel 'Chazalie'. As a result Versluys published a paper on new Hydractinia species collected by the expedition. The types are incorporated in ZMA. In 1896 he was also offered an assistantship by Prof. Weber, later continued under Prof. Sluiter. Weber was sufficiently impressed by Versluys to invite him to participate in the Siboga Expedition. He wrote two substantial Siboga monographs on gorgonarians, and his type material continues to attract the attention of contemporary specialists. Versluys got his promotion in Giessen (Germany), where he was parttime employed, sharing this with an extra-ordinary professorship at the University of Utrecht and membership of the Royal Academy of Sciences. He was a man of many interests, one of which was the study of fossil reptiles (including dinosaurs), while he also wrote authorative papers on xiphosurans (Limulus). Later in his career he was Professor of Zoology at the University of Gent (1916-1925) and from 1925 onwards Professor of Zoology at the University of Vienna (Van Bemmelen, 1935; Redeke, 1939).

Johannes Govert de Man (1850-1930) is famous for his pioneering nematode work, but like many of his contemporaries had a broad interest, including carcinology and vertebrates. He studied, graduated and promoted (1873) in Leiden, the latter on neurology and myology of birds and amphibians. From 1872-1883 he was curator of Invertebrates at the Rijksmuseum van Natuurlijke Historie at Leiden. From that date onwards he moved to Zeeland (SW Netherlands), where he worked and lived privately, first in Yerseke, later in Middelburg, pursuing various important studies. From 1909-1918 he was a curator of the Natuurlijke Historie of the Zeeuwsch Genootschap. He wrote 9 impressive Siboga Monographs on decapod crustaceans, as well as additional carcinological studies on mangrove crab and stomatopods. He also became a pioneering expert on marine freeliving nematodes and other worm groups (such as sipunculids). His material originated from the North Sea. His important collections are housed in ZMA (Van Benthem-Jutting, 1951).

H.F. Nierstrasz (1872-1937) was invited to join the Siboga Expedition as a student on recommendation from his teacher, Professor A.A.W. Hubrecht of the University of Utrecht. Nierstrasz produced Siboga Monographs on the smaller mollusc groups (chitons, parasitizing gastropods and solenogastres), on Nematomorpha, and isopods. After some years as a teacher, he succeeded Hubrecht as Professor of Zoology at the University of Utrecht in 1910, followed by a period as Rector Magnificus of that university. Together with Ihle, he wrote several authorative textbooks for university students on comparative and special zoology. He was a member of the Royal Academy of Sciences (Jordan, 1938; Strack, 1987).

Johan Egbert Willem Ihle (1879-1956) studied biology at the University of Amsterdam, where he a.o. worked on pycnogonids. He got his PhD on a thesis about Appendicularia (pelagic tunicates), and continued to work on the Siboga material of this group and the related salps and pyrosomas. This interest he kept throughout his scientific career and shared with his wife M.E. Landenberg. But he also published on parasitic nematodes and wrote a Siboga Monograph on brachyuran decapods. After a fairly long career as high school teacher combined with an assistant professorship at Professor Sluiter's laboratory, he succeeded him as Professor of Zoology at the University of Amsterdam in 1925. Together with Nierstrasz, he wrote several authorative textbooks for university students on comparative and special zoology (Barendrecht, 1956).

Jan Cornelis Christiaan Loman (1856-1929) was invited to study the Siboga Pantopoda. After graduation, he became a teacher of biology at the Amsterdam Gymnasium. He had a great influence on Heinrich Carel Redeke (1873-1945), who was to become an important authority on Dutch fisheries and freshwater biology (Engel, 1974).

Paulus Peronius Cato Hoek (1851-1914) started his studies at the Athenaeum Illustre (now the University of Amsterdam), but graduated at the University of Leiden, where he took an assistantship at the Zoological Laboratory combining it with a job as a high school teacher. He was one of the founders of the Zoological Station of the Dutch Zoological Society. At first this was a movable wooden shed, subsequently placed at various positions along the Dutch coast in order to perform local studies. Hoek was appointed director of this remarkable institute in 1887. Later it became permanently located at Den Helder, where it remained until it was renamed Netherlands Institute for Sea Research (NIOZ) and relocated on the island of Texel. Hoek was a specialist of cirripeds and pycnogonids, and such a good one that he was invited as one of the few foreign specialists to work on the collections of H.M.S. Challenger. Later he was of course also invited to work on the Siboga material of these groups. In the second half of his life he became an official state advisor on fishery matters and as such he became a member of the Permanent Council for Sea Research (later to become ICES) for which he moved to Copenhagen (Pieters & Winthagen, 1990).

H. H. Dijkstra (19xx-) is an authority of world fame on Propeamussiidae and Pectinidae (Mollusca, Bivalvia), with a publication record dozens of articles based on historical material (e.g. Linnaean and those of major international expeditions) and his own recent collections. His rich and large private collections are donated to ZMA.

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