Gymnochthebius bacchusi, Perkins, 2005

Perkins, Philip D., 2005, A revision of the water beetle genus Gymnochthebius Orchymont (Coleoptera: Hydraenidae) for Australia and Papua New Guinea, Zootaxa 1024 (1), pp. 1-161 : 1-161

Gymnochthebius bacchusi new species

(Figures 33, 34)

Type Material. Holotype (male): Papua New Guinea: Morobe District, c. 7 miles Lae ­ Bulolo Road , ex. gravel and grass roots on bank of small stream, 30 December 1964, M. E. Bacchus (MEB 120). Deposited in the BMNH . Paratypes (45): Papua New Guinea: Morobe District: Same data as holotype (36 BMNH) ; Markham Valley, Gusap, 90 mi. N.W. of Lae , ex. dead leaves on mud wetted by seepage, elev. 304 m, 27–30 January 1965, M. E. Bacchus (MEB 163) (2 BMNH) ; Markham Valley, Gusap, c. 90 mi. N.W. of Lae , large pond, muddy bottom with thick layer of dead leaves, dense Ceratophyllum , elev. 304.8 m, 27–30 January 1965, M. E. Bacchus (MEB 162) (7 BMNH) . Representative specimens to be deposited in ANIC, CMNH, FMNH, MCZ, MVMA, NMW, NPC, QMBA, QPIM, SAMA, and WAMP .

Differential Diagnosis. Recognized by the very convex form, the moderately shining

dorsum, the finely sparsely punctate pronotum, and especially the confluent pronotal anterior and posterior foveae, forming a narrow sinuate line on each side of the median groove. Distinguished from G. trilineatus , which also has confluent pronotal foveae, by the more transverse and less convex pronotum, the non­striate­impressed elytral punctures, the longer setae of the elytral punctures, and the lack of a fringe of setae on the elytral lateral margins (Figs. 29, 33). The male genitalia of the two species show some similarity, both lacking barbs, but in G. bacchusi the lobes are longer and shaped differently, the duct is more elongate, and the parameres and paramere setae differ in form (Figs. 30, 34).

Description. Size (length/width, mm) holotype: body (length to elytral apices) 1.57/ 0.69; head 0.27/0.42; pronotum 0.37/0.57; elytra 0.90/0.69. Form moderately ovate, elytra strongly convex. Color brown, head darker, dorsal reliefs shining.

Frons very finely sparsely punctate, setae obsolete; interocular foveae moderately deep; interocular tuberculi distinct; basal fovea confluent with interocular foveae. Frontoclypeal suture deeply impressed, bisinuate. Clypeus midlength 0.5 apical width, very sparsely punctate; setae very sparse on disc, distinctly denser laterally. Labroclypeal suture straight in dorsal view, evenly arcuate in anterior view. Labrum width 3x length; anterior margin arcuate, with very small apicomedian tooth.

Pronotum lateral hyaline border well developed, origin at base of lateral depression, arcuate to posterior angles, very narrow around posterior margin; anterior margin of pronotum arcuate in midregion; lateral depression wide, each with posterior angle acute point, lateral margin weakly arcuate, with short fringe of setae; lateral fossulae deep, lacking microsculpture; pronotal disc transversely moderately convex, finely sparsely punctate, most punctures with a minute recumbent seta; median groove deep, narrow, extending nearly to margins, tapering at ends; anterior and posterior foveae slightly narrower than median groove, joined by narrow channel to form slightly sinuate groove; posterolateral angles without impressions.

Elytra very convex on disc, with six rows of moderately sized punctures between suture and humeri, very weakly striate­impressed if at all; punctures with a short decumbent seta; intervals weakly rounded, if at all, width equal that of punctures; summit of declivity near midlength, where elytra are transversely markedly convex; sutural margin raised over posterior declivity; explanate margin narrow, setae recumbent, not forming fringe.

Metasternal glabrous area slightly wider than long, oval, dull, nitid, convex. Abdominal ventrites 1–3 and anteriorly 4 with hydrofuge pubescence.

Aedeagus (Fig. 34): Length of main­piece 0.28 mm, length to tip of parameres 0.31 mm; lobes very long and slender, in ventral aspect each very weakly produced apically on lateral margin, not barbed; parameres slightly widened on medial surface, apical seta elongate, ca. 2.5x length of next longest.

Females have the elytral margin similar to males, but lack the apicomedian process of the labrum.

Etymology. Named in honor of the collector, Mick Bacchus. Distribution. Currently known from Papua New Guinea. Notes. The microhabitat data can be viewed with a high level of confidence as reflecting the actual preferences of this species, since Mick Bacchus also collected ca. 3,097 Hydraena from streams in Papua New Guinea (Perkins, in prep.).