Subterranean Hydradephaga of the world: an overview (Insecta: Coleoptera)

In this review we considered stygobitic Hydradephaga, i.e. with several typical features, such as reduced or absent eyes and wings, depigmentation, and presence of sensitive setae. A total of 130 species belonging to the families Dytiscidae (122) and Noteridae (8) are distributed worldwide. In particular, among the Dytiscidae two subfamilies are represented: Copelatinae (3.3%) and Hydroporinae (96.7%). In this latter the tribe of Bidessini is the most common (55.1%), followed by those of Hydroporini (39%), Hyphydrini (0.8%), and by 5.1% of taxa listed as incertae sedis. Species description trends show a peak in the last two decades (101 species described), mainly due to the improvement of sampling methods. The analyses of the species distribution point out that 83.6% of the species come from the Australian zoogeographic region, while 87.5% of Noteridae were described from the Palaearctic region. Although few data are available for sites and collection methods, the species were collected mainly from wells (44%), through pumping (22%) and nets (19%).