It is a special pleasure for me for several reasons to write a foreword for Bernhard van Vondel’s book Adult Haliplidae of the World. First of all, I started my scientific career with my Diploma thesis on the larva of Haliplus lineatocollis, a common species of the group. Moreover, since the Handbook of Zoology Coleoptera project started in 2002, I had a very enjoyable and efficient co-operation with Bernhard van Vondel, who is the worldwide leading expert of the family. A third reason is that Haliplidae is a fascinating group, even though it is hardly known to the general public. The beetles are small, with an inconspicuous colouration, aquatic, and relatively cryptic in their environment, usually staying hidden among filamentous algae or Characeae.
Haliplidae belong to Adephaga, the second largest suborder of Coleoptera, with a total of ca. 50.000 described species, and mainly characterized by predacious habits of larvae and adults. In contrast to the typical adephagan groups like the species-rich ground beetles (ca. 40.000 spp.) and diving beetles (ca. 4.000 spp.), or also the highly specialized whirligig beetles (Gyrinidae) (ca. 1000 spp.), Haliplidae (ca. 250 spp.) mainly feed on algae as adults and exclusively as larvae, and are thus a highly unusual exception in the suborder. Despite the superficially inconspicuous habitus, haliplids display a distinctive apomorphy, greatly enlarged metacoxal plates, which almost cover the entire ventral abdomen and serve as an additional space for breathing air. The larvae are a unique case within Adephaga and beetles generally, with mandibles suitable for sucking out contents of single cells of algae, unique climbing adaptations of the fore legs, and dorsal tracheal gills or microtracheal gills unlike all other breathing organs occurring in other aquatic groups of beetles. Haliplidae are also a key taxon of Adephaga, with the systematic position disputed for a long time and arguably not fully resolved yet. Analyses of morphological data suggested either a placement as the second branch in Adephaga after Gyrinidae, or alternatively a sister group relationship to the aquatic Dytiscoidea. The latter option was finally supported by transcriptomic analyses.
Adult Haliplidae of the World will certainly be tremendously useful for everybody collecting or investigating Haliplidae. The keys to the genera and species of the family are very useful for identifying specimens from all corners of the planet. An outstanding feature of the book is that it is magnificently illustrated, with numerous excellent morphological line drawings, all of them prepared by the author himself. In addition, habitus photos are provided, and also distribution maps. Precise diagnoses are given for all species, with additional information on the biology, habitats, immature stages, and distribution. The rich information presented in the book is certainly an example that should be followed by enthusiasts of other groups of Coleoptera.
All in all, I can only praise this work of Bernhard van Vondel, who has dedicated decades of study to an often underestimated but nevertheless fascinating group of Coleoptera.