Six new species of New Guinea Exocelina Broun, 1886 are described in this paper: E. iratoi sp. n., E. likui sp. n., E. pui sp. n., E. pulukensis sp. n., E. tomhansi sp. n., and E. wigodukensis sp. n. Although different morphologically, together with Exocelina ascendens (Balke, 1998), E. bagus (Balke & Hendrich, 2001), and E. ransikiensis Shaverdo, Panjaitan & Balke, 2016, they are found to form a monophyletic clade and be closely related to representatives of the E. ekari-group, based on preliminary analysis of sequence data. An identification key to the species is provided, and important diagnostic characters are illustrated. The present data on the species’ distribution show that most of them are local endemics.

Background The New Guinean archipelago has been shaped by millions of years of plate tectonic activity combined with long-term fluctuations in climate and sea level. These processes combined with New Guinea’s location at the tectonic junction between the Australian and Pacific plates are inherently linked to the evolution of its rich endemic biota. With the advent of molecular phylogenetics and an increasing amount of geological data, the field of New Guinean biogeography begins to be reinvigorated. Results We inferred a comprehensive dated molecular phylogeny of endemic diving beetles to test historical hypotheses pertaining to the evolution of the New Guinean biota. We used geospatial analysis techniques to compare our phylogenetic results with a newly developed geological terrane map of New Guinea as well as the altitudinal and geographic range of species (https://arcg.is/189zmz). Our divergence time estimations indicate a crown age (early diversification) for New Guinea Exocelina beetles in the mid-Miocene ca. 17 Ma, when the New Guinean orogeny was at an early stage. Geographic and geological ancestral state reconstructions suggest an origin of Exocelina ancestors on the eastern part of the New Guinean central range on basement rocks (with a shared affinity with the Australian Plate). Our results do not support the hypothesis of ancestors migrating to the northern margin of the Australian Plate from Pacific terranes that incrementally accreted to New Guinea over time. However, our analyses support to some extent a scenario in which Exocelina ancestors would have been able to colonize back and forth between the amalgamated Australian and Pacific terranes from the Miocene onwards. Our reconstructions also do not support an origin on ultramafic or ophiolite rocks that have been colonized much later in the evolution of the radiation. Macroevolutionary analyses do not support the hypothesis of heterogeneous diversification rates throughout the evolution of this radiation, suggesting instead a continuous slowdown in speciation. Conclusions Overall, our geospatial analysis approach to investigate the links between the location and evolution of New Guinea’s biota with the underlying geology sheds a new light on the patterns and processes of lineage diversification in this exceedingly diverse region of the planet.

Two new species of the genus Exocelina Broun, 1886: E. athesphatossp. nov. and E. tsingasp. nov. are described from New Guinea and placed into the E. ekari group based on the structure of their male genitalia. The two species are very similar with respect to their external morphology and characterised by almost identical, strongly modified male antennae. However, they can easily be separated by the shape and setation of the median lobe and paramere. Based on morphological similarity and results of a molecular phylogenetic analysis, we suggest these are sister species. Both of them have been collected on the southern slopes of the Central Range (the spine of New Guinea), with a distance of ca. 380 km straight line between the collecting localities.

Seven new species of the genus Exocelina Broun, 1886 are described from three different mountain ranges of New Guinea: E. fojasp. nov., E. riberaisp. nov., E. apisteftisp. nov., and E. waafsp. nov. from the Foja Mountains; E. hudsonisp. nov. from the Cyclops Mountains; E. ekpliktikisp. nov. and E. oraiasp. nov. from Wano Land. All of them are placed into the E. ekari group based on the structure of their male genitalia. The species are characteristic dytiscid elements of the fauna of northern cost and the western part of central orogen of New Guinea. Two taxonomic notes are presented: Exocelina athesphati is a correct name for the recently described Exocelina athesphatos Shaverdo et al., 2020; Exocelina bacchus Balke, nom. nov. is a replacement name for Exocelina bacchusi (Balke, 1998), formerly Copelatus (Papuadytes) bacchusi Balke, 1998, a junior homonym of Copelatus bacchusi Wewalka, 1981.

Two new species and one new subspecies of Exocelina Broun, 1886 from New Guinea are described: E. okbapensis Shaverdo & Balke, sp. n., E. okbapensis hajeki Shaverdo & Balke, ssp. n., and E. may Shaverdo & Balke, sp. n. These and two already described species are assigned to the E. okbapensis-group, which is morphologically (based on setation of the paramere) and phylogenetically close to the E. aipogroup. On the latter, morphological and taxonomic notes are provided. An identification key to all known species of the groups is presented, and important diagnostic characters are illustrated. Data on the species distributions are mapped and show that the species occur only in the central mountain part of the island restricted by Wamena in the west and Sandaun Province in the east.