Hydraena Kugelann, 1794

Hydraena Kugelann, 1794: 578 (type species Hydraena riparia Kugelann 1794: 579).

The hyperdiverse, cosmopolitan genus Hydraena is well defined by the following autapomorphic morphological characteristics: 1) presence of a labral-mandibular interlocking device (Perkins 1989), 2) mentum with an acute median projection anteriorly (Perkins 1989), 3) various complex sensilla (Perkins 1997), and 4) specialized features of the exocrine secretion delivery system (Perkins 1997). There is general agreement among current workers that Hydraena is monophyletic, based on these morphological characters (for example, Jäch et al. 2000).