Book Review

Holoplanktonic Mollusca include Pteropoda and Heteropoda that live their entire life as plankton in the water column of the sea. They have been studied already for a considerable time by well known Dutch malacologists. Between 1903 and 1950, J.J. Tesch (1877-1954) published on pteropods from the Siboga, Snellius and Dana expeditions. For his PhD thesis (1967), S. van der Spoel worked on shell-bearing pteropods (Euthecosomata). He published a supplementary magnum opus on the Pseudothecosomata, Gymnosomata and Heteropoda in 1976, apart from a long series of smaller publications on these molluscs. Arie W. Janssen, author of this book, became well known for his work on Dutch Neogene molluscs as co-author in the series on fossil shells from Dutch beaches and inlets published in Basteria, and as the author of the ‘bible’ for many (amateur) collectors of Miocene shells in the Netherlands: “Mollusken uit het Mioceen van Winterswijk-Miste”, published in 1984. Since about 1980, Arie Janssen has specialised in Neogene holoplanktonic gastropods. As planktonic organisms these were often widely distributed and many species lived for only a relatively short timespan. This makes them extraordinary important for stratigraphy to correlate sediments deposited in different parts of the world. A correct identification of the species is, of course, of utmost importance for correlations to be valid. One of the problems in identification of species is that one often has to go back to the first descriptions, dating from the 19th century. These are usually too short, lacking important information, pictures are often insufficient, no type material was indicated and the original material is sometimes even lost.