Andersen, N. M.: Early evolution of a unique structure: a fossil water measurer from Baltic amber (Hemiptera: Gerromorpha: Hydrometridae). Insect Syst.Evol.34: 415-426. Copenhagen, December 2003. ISSN 1399-560X.
Water measurers, genus Hydrometra Latreille (Hemiptera-Heteroptera, Hydrometridae) represent a unique morphological type in insects, with their extremely prolonged head and thorax. The fossil record of the family is more extensive than for any other group of semiaquatic bugs (infraorder Gerromorpha), spanning more than 120 Myr of geological history. A new fossil from Baltic amber yields characters that can be used to place it in the extant genus Hydrometra, the most species-rich and widely distributed of all genera of Hydrometridae. The phylogeny of extant and extinct genera is reconstructed and the evolution of the unique head and thorax structure of water measurers is discussed.