The simple exposition of phylogenetic study in Hydradephaga

Key Words：Hydradephaga, phylogeny, classification

Abstract：　　Hydradephaga belonging to the Coleoptera, is a kind of true water beetles with aquatic flesh-eating habits. In the classification system in the true water beetles, there are three hypotheses, one is suborder Adephaga at the base of the system, the second is suborder Polyphaga at the base, and the third is suborder Myxophaga at the base. More recent studies tend to the first hypothesis. At present, Hydradephaga are about 5 500 species, more than 200 genera, with 8 families. Although the phylogenetic relationships of Hydradephaga have been extensively studied, the view is not uniform. There are three representative hypothesis, first, Gyrinidae is at the base of the system, followed by Dytiscidae, Amphiziodae, Hygrobiidae, Noteridae and Haliplidae; Second, Haliplidae is at the base; Third, Gyrinidae is at the base, followed by Haliplidae and Dytiscoidea, of which is made up of Dytiscidae，Amphiziodae，Hygrobiidae and Noteridae. At present, according to the morphological and molecular classification methods, the third hypothesis is more than representative in the classification system of Hydradephaga, and also supports a hypothesis which their ancestors as a monophyletic groups is from land.