Gymnochthebius nigriceps, 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 nigriceps new species

(Figures 50, 51, 92)

Type Material. Holotype (male): Australia: South Australia: In runoff from Mound Spring near Coward Springs , 29° 24' S, 136° 47' E, 3 March 1975, E. W. Matthews. Deposited in the SAMA . Paratypes (38): Australia: South Australia: 36 km ESE of Curdimurka , 29° 36' S, 137° 26' E, 21 September 1972, J. Upton (1 ANIC) ; 6 km SE Blanche Cup, Mound Springs , spring, 29° 24' S, 136° 47' E, 16 May 1981, J. A. Forrest (6 SAMA) ; In runoff from Mound Spring near Coward Springs , 29° 24' S, 136° 47' E, 3 March 1975, E. W. Matthews (31 SAMA) . Representative specimens to be deposited in MCZ, NPC, QMBA, and WAMP .

Differential Diagnosis. Recognized by the black head contrasting with the testaceous to light brown pronotum and elytra, the lack of a prominent setal fringe on the elytral margin, and the weakly shining or dull dorsum. Sharing with G. fontinalis the anteriorly extended lateral hyaline border, the distinctive abdominal hydrofuge pattern where the hair­line forms a very discrete arc on the fifth ventrite, and the females having a spinose last tergite. Differing from G. fontinalis in having the pronotal disc less coarsely punctate, the dorsum slightly more convex, the body slightly wider and less parallel­sided, the coloration, and in females the arcuate last tergite (Figs. 50, 52). The male genitalia of the two species also show a relationship, but differ significantly in several features, including lobe and duct shapes, and the shorter length in G. nigriceps (Figs. 51, 53).

Description. Size (length/width, mm) holotype: body (length to elytral apices) 2.12/ 0.90; head 0.33/0.48; pronotum 0.48/0.71; elytra 1.34/0.90. Form moderately ovate, moderately convex. Pronotum, elytra and appendages testaceous, head black. Dorsum dull or weakly shining.

Head with frons coarsely punctate on disc, microreticulate throughout, setae recumbent, long and yellowish; interocular foveae shallow; interocular tuberculi indistinct; basomedial fovea shallow, confluent with interocular foveae. Frontoclypeal suture moderately deeply impressed, bisinuate. Clypeus midlength 0.5x apical width, moderately punctate on disc, microreticulate throughout; pubescence on disc similar to frons. Labroclypeal suture straight in dorsal view, evenly arcuate in anterior view. Labrum width slightly greater than twice length, anterior margin shallowly emarginate. Maxillary palpomere 3 three times length of 4.

Pronotum lateral hyaline border well developed, origin at anterior 0.33 of lateral depression, margin straight, then arcuate at posterior angles, narrow around posterior margin; anterior margin of pronotum straight or weakly arcuate in midregion; each lateral depression microreticulate, punctate and with yellowish setae, lateral margin more densely setose, lateral margin produced in obtuse point at about midlength, posterior angle acute; lateral fossulae moderately deep, microreticulate; pronotal disc weakly convex, moderately coarsely, moderately densely punctate, each puncture with a recumbent yellow seta; median groove shallow, narrow, extending nearly to margins, tapering at ends; anterior foveae well developed, oval; posterior foveae shallow, oblique, 1/2 as long as and twice as wide as median groove; posterolateral angles without impressions.

Elytra elongate, weakly convex on disc, with six rows of closely spaced punctures between suture and humeri, each puncture with a yellowish recumbent seta; intervals flat, effacedly microreticulate, width twice that of punctures, punctures round, separated from each other by 0.5–1.0x puncture width; posterior declivity gradual, summit at about 0.66 of length; striae 2 and 3 terminating into 4 at about apical 1/4; elytral explanate margin very narrow, with short decumbent indistinct setae, not forming a fringe.

Metasternal glabrous area longer than wide (as 20:15), elongate oval, shining, convex. Abdominal ventrites 1–4 and part of 5 with hydrofuge pubescence; on 5 pubescence laterally and basally, forming a very discrete arc­shaped non­pubescent area.

Aedeagus (Fig. 51): Length of main­piece 0.47 mm, paramere tips very slightly beyond tips of lobes; lobes relatively long, not barbed, apically roundly acute; ventral notch V­shaped, with sinuate margins, dorsal notch wider, U­shaped; duct asymmetrical, apically pointed in ventral aspect, truncate in lateral aspect; paramere setae clustered at and near apex, apical setae short, longest seta ca. 2x length of next longest.

Females have the explanate elytral margin markedly arcuate, about twice as wide as it is in males, as wide as the mesotibia; the elytral sutural margins are sometimes weakly emarginate just before the apices, forming a narrow gap between the elytra; the anterior margin of the labrum is apicomedially weakly emarginate; the last abdominal tergite has a prominent fringe of spine­like setae.

Etymology. Named in reference to the dorsal coloration.

Distribution. Currently known from two closely spaced localities in central South Australia (Fig. 92).