Petrodessus, Miller, Kelly B., 2012

Miller, Kelly B., 2012, Petrodessus conatus sp. n., a new genus and species of Bidessini from hygropetric habitats in tropical Australia (Coleoptera: Dytiscidae: Hydroporinae), Zootaxa 3242, pp. 62-67 : 63-64

Petrodessus n. gen.

( Figs 1–14 )

Type species. Petrodessus conatus sp. n., by monotypy.

Diagnosis and description. This genus differs from others in the tribe by the combination of: 1) transverse occipital line absent ( Fig. 1 ), 2) basal pronotal striae present, basally deeply impressed with a shallow, transverse groove connecting the striae ( Fig. 1 ), 3) basal elytral stria present, basally deeply impressed ( Fig. 1 ), 4) elytral sutural stria absent, 5) anterior clypeal margin strongly flattened, anteriorly produced, with broad anterior margin ( Fig. 1 ), 6) elytron without longitudinal carinae ( Fig. 1 ), 7) epipleuron without transverse carina at humeral angle, 8) lateral lobes of aedeagus two-segmented (Figs 5,6), and 9) protibia broadly triangular, heavily spinous ( Fig. 2 ). Individuals have relatively few natatory setae on the legs, which are robust and spinous, in general (Figs 2,3).

Etymology. The genus name is formed from a combination of petro, Greek for “rock”, and dessus, a common root in other genus names in this tribe to signify the rock-surface habitat of the single member of the genus. The gender of the name is masculine.

Distribution. Petrodessus n. gen. is known from the following newly described species from Tully Gorge and Paluma Range National Parks in the Misty Mountains and Paluma Mountain Range of Australia ( Fig. 8 ).

Discussion. This genus keys to couplet 14 in Biström’s (1988) key to the Bidessini genera of the world where it does not fit either choice, Microdessus Young, 1967 or Uvarus Guignot, 1939 . It can be easily distinguished from each of these taxa by the prominently flattened and produced anterior clypeal margin ( Fig. 1 ). Balke and Ribera (2004) pointed out the problems with using the transverse occipital line as a diagnostic character for genera within Bidessini contending that it exhibits considerable homoplasy in the group. Presence or absence of this feature appears in an early couplet (#4) in Biström’s (1988) key. When Petrodessus n. gen. is run through that part of the key with taxa that have an occipital line present, it keys out to Neoclypeodytes Young, 1967 , a Nearctic group. Petrodessus n. gen. bears some resemblance to Neoclypeodytes and also Clypeodytes Régimbart, 1894 , Leiodytes Guignot, 1936 and Borneodessus Balke, Hendrich, Mazzoldi & Biström, 2002 . From Clypeodytes, Petrodessus n. gen. differs in the lack of a transverse epipleural carina at the humeral angle, the lack of any longitudinal carinae on the elytra, and the lack of a transverse occipital line. The genus differs from Leiodytes in lacking rows of punctures on the medial portion of the metasternum. From Borneodessus, Petrodessus n. gen. differs especially in the lack of the basal elytral striae in the former taxon. The similarity to Neoclypeodytes in characters is more pronounced, though Neoclypeodytes itself has taxa with character combinations making discrete definition of that genus problematic, as well ( Miller, 2001), and Petrodessus n. gen. is superficially quite different. Rather than expanding Neoclypeodytes to include this new species, which lacks one of the few consistent features within Neoclypeodytes (the transverse occipital line), it seems best to put this species in its own genus until a more thoroughgoing clarification of the genus-level classification in the large and problematic Bidessini can be established.

Figures

FIGURE 8. Petrodessus conatus sp. n., distribution.

FIGURES 1 – 7. Petrodessus conatus sp. n. 1) Dorsal habitus. 2) Left proleg, anterior aspect. 3) Left metaleg, anterior aspect. 4) Male median lobe, right lateral aspect. 5) Male right lateral lobe, right lateral aspect. 6) Male median lobe and right lateral lobe, ventral aspect. 7) Female genitalia, ventral aspect. Scale bar = 1.0 mm for 1 – 3 only.

FIGURES 9 – 14. Petrodessus conatus sp. n., habitats. 9 – 11) Paluma Range National Park, Twin Falls site (10 close-up). 12, 13) Tully Gorge National Park site. 14) Paluma Range National Park, Twin Falls site, close-up of specimen on habitat.