Austrelatus gen. nov., a new genus of Australasian diving beetles (Coleoptera, Dytiscidae, Copelatinae), with the discovery of 31 new species from New Guinea.

Herein, (type species: W.J. Macleay, 1871) is described for a distinctive lineage of predominantly Australasian species previously assigned to Erichson, 1832. The new genus was retrieved as well supported, monophyletic clade in phylogenetic analysis of DNA sequences data using Bayesian and parsimony approaches. The main morphological diagnostic character of is a complex median lobe of the aedeagus, with evident dorsal and ventral sclerites usually divided in apical half into two lobes of different shape or otherwise modified. Morphological comparison of the new genus with other Copelatinae genera, especially with and Broun, 1886, and a generic key to the New Guinean Copelatinae are provided. New combinations are established for 31 already described species mainly from the Australian Region (all from ): (Megna, Atthakor, Manaono, Hendrich & Balke, 2017), ; (Sharp, 1882), ; (J. Balfour-Browne, 1939), ; (Hájek, Shaverdo, Hendrich & Balke, 2021), ; (Hájek, Shaverdo, Hendrich & Balke, 2021), ; (Hendrich & Balke, 1998), ; (Sharp, 1882), ; (Sharp, 1882), ; (Wewalka, 2017), ; (Sheth, Ghate & Hájek, 2018), ; (Zimmermann, 1928), ; (Régimbart, 1892), ; (W.J. Macleay, 1871), ; (Guignot, 1956), ; (Hájek, Shaverdo, Hendrich & Balke, 2021), ; (Hájek, Shaverdo, Hendrich & Balke, 2021), ; (Guignot, 1956), ; (Sheth, Ghate & Hájek, 2018), ; (Zimmermann, 1919), ; (Sharp, 1882), ; (J. Balfour-Browne, 1939), ; (Zimmermann, 1920a), ; (Hendrich & Balke, 1998), ; (Hájek, Hendrich, Hawlitschek & Balke, 2010), ; (Fairmaire, 1878), ; (Régimbart, 1899), ; (Hendrich & Balke, 1995), ; (Hájek, Shaverdo, Hendrich & Balke, 2021), ; (Hájek, Shaverdo, Hendrich & Balke, 2021), ; (J. Balfour-Browne, 1939), and (Régimbart, 1899), species from New Guinea are divided into two informal species groups, the group and group, and and standing aside of them. The group is introduced with three previously known species and 29 new species described here based on the morphological characters and Cox1 data: , , , , , , , , , , , , , , , , , , , , , , , , , , , , and Zimmermann, 1919, is recognised as a junior subjective synonym of (Sharp, 1882). The lectotypes of Régimbart, 1892, Zimmermann, 1919 and Régimbart, 1899 are designated. All species are (re)described, and their important species characters (genitalia, habitus, and colour patterns) are illustrated. Keys to all species are provided. The known distribution and habitat preferences of each species are outlined briefly. New Guinean occupy a variety of stagnant water habitats, either lentic , or standing water associated with lotic habitats (e.g., backflows, rockpools, intermittent / ephemeral stream pools).