Kakadudessus tomweiri, a new genus and species of diving beetle from tropical northern Australia, based on molecular phylogenetic and morphological data (Coleoptera, Dytiscidae, Bidessini) Author Hendrich, Lars Author Balke, Michael text Zootaxa 2009 2134 49 59 journal article 10.5281/zenodo.188458 61fa4cb4-d546-480f-b6d1-5f7590fc265d 1175-5326 188458 Kakadudessus gen.n. ( Figs 1–5 ) Type species: Kakadudessus tomweiri Hendrich & Balke by current designation (monotypy). Diagnosis and description: Kakadudessus is assigned to the Bidessini based on the bi-segmented parameres of the aedeagus ( Figs 3–4 ) ( Biström 1988 ). It differs from all other Bidessini by the combination of the following characters: 1) Habitus elongated, almost flat, with pale yellowish markings on elytra ( Fig. 1 ), 2) head with cervical line and clypeus anteriorly bordered, 3) pronotum and elytra with well developed striae, ( Fig. 1 ), 4) elytra without keels, without sutural line and without accessory striae, 5) posterior part of basal cavity of epipleura without a transverse carina, 6) prosternal process reaching metaventrite, laterally margined and fairly elongate and narrow, 7) metaventrite with rows of punctures at midline and metacoxal lines longer than distance between them, strongly diverging anteriorly, 8) parameres two segmented, very thin, slender and elongate, only very slightly bifid anteriorly ( Figs 4–5 ). According to Biström (1988) and Pederzani (1995) the genus keys out to Limbodessus Guignot, 1939 , Leiodytes and Uvarus Guignot, 1939 ; the parameres resemble those of species of Allodessus Guignot, 1953 . Limbodessus , at least the epigean species, have a strongly two-fingered distal paramere segment; Allodessus appears similar but does not have an anteriorly bordered clypeus ( Biström, 1988 ). Australian species of the genus Uvarus and the related genus ( Fig. 7 ) Gibbidessus Watts, 1978 are constantly smaller (TL = 1.1–2.1 mm ) and have a more roundish body. Furthermore, Gibbidessus does not have an anteriorly boderded clypeus and Uvarus is lacking a cervical line on clypeus. Parameres of both genera are broader and not bifid anteriorly. Thus, it remains unclear, based on morphological characters, to which genus to assign the new species. Ambiguity related to the use of morphological characters for the generic classification of Bidessini has been expressed before, a good example being the lack of a cervical line in some but not all species of Limbodessus (in part in Biström 1988 ; Balke & Ribera 2004 and Miller & Spangler 2008 ). Therefore, we used DNA sequence data to place our new species and test if it, for example, represents a derived member of Limbodessus or Allodessus . Molecular systematics: Our analysis shows ( Fig. 7 ) that Kakadudessus is neither part of the Allodessus / Limbodessus nor the Leiodytes / Clypeodytes clades. It is rather part of a separate lineage sister to the former clades. This lineage includes the Australian Gibbidessus and Uvarus . It remains a contentious issue when and whether to merge or split genera. In this case, to avoid paraphyly assigning our new species to either Gibbidessus or Uvarus , one had to classify all species in this clade as Uvarus , being the oldest available genus name. To accommodate morphological differences, we suggest to introduce the new genus Kakadudessus for our new species. Etymology: Kakadudessus refers to the Kakadu National Park, an important and diverse refuge for water beetles in Australia and one of the type localities, plus - dessus , a common root for many generic names in the tribe Bidessini (see Miller & Spangler 2008 ). Distribution and habitat: The genus is known from five sites, three in the Northern Territory and two in north-eastern Queensland. At all sites the population density of the species was quite low and it was not possible to collect more than six specimens at one site. A detailed habitat description and the associated rich dytiscid fauna is given below.