Petrodessus conatus, 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 : 65-66

Petrodessus conatus sp. n.

( Figs 1–14 )

Type locality. Australia, Queensland, Paluma Range National Park, Twin Falls, 19°0.483'S 146°14.333'E.

Material examined. HOLOTYPE: m# in the Queensland Museum labeled, “ Australia, Queensland, Paluma Range NP, TwinFalls 19º 0.483'S 146º 14.333'E 19 Mar 2011, KB Miller, leg. KBM 19031101 rock seeps", " Holotype Petrodessus conatus K.B. Miller, 2011 " [red label with black line border]. PARAPTYES: 160 same collecting labels as holotype; 16 labeled, “ Australia, Queensland Paluma Rng NP, nr Crystal Ck 19º0.922'S 146º15.988'E 18 Mar 2011, KB Miller, leg. KBM 18031102 rock seeps.”; 19 labeled “AUS, Qld, Tully Gorge NP, at Frank Roberts Lookout, 19Mar2011 17º46.706'S 145º39.052'E KB Miller, leg. KBM 19031102 rock seeps.”. All paratypes with “ Paratype Petrodessus conatus K.B. Miller, 2011 ” [red label with black line border].

Diagnosis. Petrodessus conatus sp. n. is the only member of this genus and is characterized by the diagnostic features of Petrodessus n. gen. Likely species level diagnostic features include the coloration, which is uniformly red-brown to yellow-brown, and the shape of the male genitalia with the male median lobe in lateral aspect elongate and slender and evenly and shallowly curved to the pointed apex ( Fig. 4 ) and in dorsal aspect moderately broad basally and medially and then tapered to a pointed apex ( Fig. 6 ).

Description. Measurements. TL = 1.5–1.7 mm, GW = 0.8–1.0 mm, PW = 0.7–0.8 mm, HW = 0.5–0.6 mm, EW = 0.2–0.3 mm, TL/GW = 1.7–1.8, TL/PW = 1.1–1.2. Body broad, robust, globular ( Fig. 1 ); lateral outline slightly discontinuous between pronotum and elytron ( Fig. 1 ); lateral margins of pronotum broadly and evenly curved ( Fig. 1 ); lateral margins of elytron broadly curved ( Fig. 1 ).

Coloration. Head anteriorly yellow, broadly yellow-brown posteriorly and near eyes; pronotum yellow on anterolateral surfaces, medially and posteriorly yellow-brown; elytron uniformly brown, epipleuron yellow; legs and appendages yellow; ventral surfaces yellow-red to red-brown.

Sculpture and structure. Head with fine, inconspicuous, irregular punctation, surface between punctures with fine, inconspicuous microsculpture; eyes medium in size ( Fig. 1 , HW/EW = 1.6–1.8); anterior margin of clypeus distinctly produced anteriorly, flattened and distinctly beaded ( Fig. 1 ). Pronotal surface similar to that of head; with posterior angles obtuse; lateral bead narrow, of even width throughout ( Fig. 1 ); pronotal striae prominent, extending about 1/4 distance across pronotum, region mediad to striae deeply impressed ( Fig. 1 ). Elytron with anterolateral angle obtuse, not extended anteriorly; surface similar to pronotum; basal stria prominent, shorter than length of pronotal striae, region mediad to striae deeply impressed ( Fig. 1 ). Prosternal process narrow, apically pointed, apically contacting metaventrite, lateral margins convergent to apex; metacoxal process with lateral lobe minute but distinct; metaventrite finely, sparsely punctate, metacoxa more coarsely punctate medially. Pro- and mesotarsi moderately broad in male, slightly narrower in female. Metatrochanter large relative to metafemur ( Fig. 3 ).

Male genitalia. Median lobe in lateral aspect elongate, slender, of even width, evenly curved to pointed apex ( Fig. 4 ); in ventral aspect moderately broad in basal half, apically evenly tapered to narrowly pointed apex ( Fig. 6 ). Lateral lobe in lateral aspect elongate and relatively slender, apical half of even width, elongate, apically broadly rounded with small medial hook, dorsal margin with series of elongate setae ( Figs 5, 6 ).

Etymology. This species is named conatus, Latin for “endeavor” in honor of the HMS Endeavor, Captain James Cook’s ship in which he led the first European expedition to make contact with the east coast of Australia. The specific epithet is a noun in the nominative singular standing in apposition.

Habitat and natural history. This species appears to be exclusively hygropetric on water seeps on rock faces that are vertical, nearly vertical, or even overhanging ( Figs 9–14 ). Specimens were collected in algal matts on the rock surface ( Fig. 14 ), but also often on bare rock where they seemed to take refuge in cracks or behind pieces of debris. In some cases they were densely concentrated and abundant, but in others they were relatively sparsely distributed. Large numbers of specimens were collected only from nearly vertical to overhanging surfaces. Specimens were easily found and collected at night simply by examining the wet surfaces. However, they were more easily seen and collected using permethrin fogging which resulted in agitation of the specimens which then moved about. Specimens were found among numerous Trichoptera and Scirtidae larvae as well as Hydraenidae and Hydrophilidae specimens. Considerable water in different habitats was available near the sites of collection including large, torrential rivers, medium to small streams, waterfalls, and small standing water bodies. Although other diving beetles were found in these habitats, no Petrodessus were found there.

Interestingly, two of the few known terrestrial diving beetles, Terradessus caecus Watts, 1982 , and T. anophthalmus Brancucci & Monteith, 1997 (possibly members of Bidessini ) were discovered in this same wet tropical bioregion of Australia ( Watts 1982, Brancucci & Monteith, 1997). The boundary between aquatic and terrestrial habitats in wet tropical areas can be relatively vaguely delimited. This area of Australia may be, therefore, particularly suitable for studying evolutionary transitions between aquatic and terrestrial trophic zones through intermediate habitats such as those with Petrodessus .

Figures

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.

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

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.