Gymnochthebius Orchymont, 1943

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 Orchymont, 1943

Ochthebius (Gymnochthebius) Orchymont, 1943: 38 (type species Ochthebius nitidus LeConte, 1850 ).

Gymnochthebius: Perkins, 1980: 244 (New World species).

Gymnochthebius: Perkins, 1997: 126 (behavior, morphology, classification).

Description. Form generally elongate oval, some members sub­truncate, moderately to strongly convex. Size length/width (mm) varying from about 2.24/1.00 to 1.20/0.64. Females generally slightly larger than males. Color testaceous to brown to black, dorsum sometimes with metallic reflections.

Head varied from nearly impunctate and shiny to coarsely punctate and markedly microreticulate. Interocular foveae moderately developed. Interocular tuberculi (ocelli) evident. Clypeus length of most adults 1/2 width, sides convergent anteriorly. Labrum of most males upturned apicomedially, less so or not upturned in females. Maxillary palpus short, palpomere 3 distinctly thickened. Mentum width generally equal length, anterior margin straight or slightly arcuate to rear. Genae shining, swollen. Antennomeres nine (4 + 5).

Pronotum with well developed lateral hyaline margin, sclerotized portion varied from non­incised in anterior 1/2 to deeply incised. Anterior margin usually slightly bisinuate in habitus view, anterior angles often lobe­shaped. Lateral depressions usually impressed for length of pronotum, infrequently reduced to small foveae at anterior. Pronotal disc usually with well developed anterior and posterior foveae, and median groove; infrequently posterior foveae and median groove obsolete. Prosternum with median carina ended at coxal cavities; coxae contiguous. Metasternum hydrofuge pubescent in midregion or not. Elytra generally with six prominent rows of punctures between suture and humeri, each puncture with a seta; setae usually slender, infrequently widened and flattened; serial punctures infrequently absent or greatly reduced; microreticulation varied from very coarse to absent. Explanate margin varied, sometimes with distinctive fringe of setae.

Abdomen with hydrofuge pubescence on ventrites varied, usually first five pubescent, sometimes reduced to first four, first three or first two. Ventrite seven frequently with admedian row of setae. Legs varied from moderately long and slender to short and stout, spines varied from thin and dense to stout and sparse. Males without distinctive protarsal pads of suction setae; metatibiae unmodified. Aedeagus with main­piece bifid, internal structure tubuliform or cupuliform, placed in lumen between forks; parameres varied in length, usually extended slightly beyond main­piece, sometimes extending well beyond, and infrequently terminating at level of tips of main­piece. Spermatheca varied.

Antennal pocket (terminology as in Perkins, 1997) hypomeral, wide, smooth except for anteromedial asperite hydrofuge area. Hypomeral, lateral, anterior, and posterior hyaline borders all well developed. Hypomeral antennal pocket setae comparatively long, extending beyond the hypomeral hyaline border. Wet hypomeron small. Postocular area near posteroventral angle of eye with secretion sulcus and slender, arcuate secretion delivery setae. Genal hydrofuge asperite. Periocular pores present adjacent to the eye facets.