Decarthrocerus bambusicus, Perkins, 2009

Perkins, Philip D., 2009, Revisions of the genera Parhydraena Orchymont, Protozantaena Perkins, Decarthrocerus Orchymont, and Parhydraenopsis nomen novum, aquatic and humicolous beetles from Africa and Madagascar, and comparative morphology of the tribe Parhydraenini (Coleoptera: Hydraenidae), Zootaxa 2038, pp. 1-119 : 54-55

Decarthrocerus bambusicus new species

( Figs. 1, 29, 85, 87, 103)

Type material. Holotype (male): Democratic Republic of Congo: P. N. Virunga, Volcan Sabinyo , Chanya W., W. Sabinyo: Tshamugussa, tamisage sous bambous, 1° 23' S, 29° 35' E, vii.1964, R. P. Celis. Deposited in the MRAC . Paratypes (94): Democratic Republic of Congo: Kivu, Uvira, haute Sange , foret de bambous, recolte dans l'humus, elev. 2500 m, 3° 24' S, 29° 0' E, ii.1951, N. Leleup (1 MRAC) ; Kivu, Uvira, hte. Luvubu , foret de bambous, recolte dans l'humus, elev. 2650 m, 3° 24' S, 29° 0' E, 10.xi.1950, N. Leleup (1 MRAC) ; P. N. Virunga, Volcan Mikeno , E de Rweru, tamisage, elev. 2750 m, 1° 28' S, 29° 25' E, 5.vii.1964, R. P. Celis (9 MRAC) ; P. N. Virunga, Volcan Mikeno, Rweru , tamisage, elev. 2900 m, 1° 28' S, 29° 25' E, 30.vi.1964, R. P. Celis (13 MRAC) ; P. N. Virunga, Volcan Mikeno, Rweru , tamisage, bambousaie, elev. 2800–2900 m, 1° 28' S, 29° 25' E, 21.vi.1964, R. P. Celis (8 MRAC) ; P. N. Virunga, Volcan Mikeno, Rweru- Kabara , tamisage, 1° 28' S, 29° 25' E, 30.vi.1964, R. P. Celis (4 MRAC) ; P. N. Virunga, Volcan Mikeno, Rweru-Kibumba , tamisage bambousaie, elev. 2580 m, 1° 28' S, 29° 25' E, 25.vi.1964, R. P. Celis (9 MRAC) ; P. N. Virunga, Volcan Mikeno , SE de Rweru, tamisage bambousaie, elev. 2800 m, 1° 28' S, 29° 25' E, 26.vi.1964, R. P. Celis (2 MRAC) ; P. N. Virunga, Volcan Mikeno , SW de Rweru, tamisage, elev. 2550 m, 1° 28' S, 29° 25' E, 29.vi.1964, R. P. Celis (9 MRAC) ; P. N. Virunga, Volcan Sabinyo, Chanya W., W. Sabinyo: Tshamugussa , tamisage sous bambous, 1° 23' S, 29° 35' E, vii.1964, R. P. Celis (9 MRAC) ; P. N. Virunga, Volcan Sabinyo, SE Tshamugussa , tam. sous bambous, elev. 2300 m, 1° 23' S, 29° 35' E, 16.vii.1965, R. P. Celis (5 MRAC) ; Zaire, Kivu, P. Nat. Kahuzi-Biega, Bambuswald , 2° 0' S, 28° 45' E, 13.ii.1984, H. Mühle (11 NMW) ; Kivu Province, Kivu: Itombwe, Tete de source Kahololo , humus tourbiere sous buissons, elev. 2800 m, 3° 30' S, 28° 55' E, i.1960, N. Leleup (B. 120) (7 MRAC) ; Rwanda: Pref. Cyangugu, Diauma, Gisoma , 2° 30' S, 29° 10' E, 21.i.1986, H. Mühle (1 NMW) ; Pref. Cyangugu, Umg. Nyakabuye , 2° 10' S, 29° 31' E, 17.ii.1985, H. Mühle (1 NMW) ; same locality, 2° 10' S, 29° 31' E, 9.vi.1985, H. Mühle (4 NMW) .

Differential diagnosis. Distinguished among other members of the genus by the circular metaventral impression, the slightly longer maxillary palpi (palpus length/head width ca. 0.43), and the smaller body size (length ca. 2.17 mm) ( Fig. 85). The aedeagus indicates a relationship with D. mbizi ( Figs. 85, 88).

Description. Size (length/width, mm) holotype: body (length to elytral apices) 2.17/0.93; head 0.31/0.63; pronotum 0.52/0.89, PA 0.71, PB 0.65; elytra 1.33/0.93. Color dark brown to piceous; maxillary palpi light brown; dorsum with stiff, arcuate, yellow setae (dorsum usually thickly coated with debris).

Head with eyes small in dorsal aspect, ca. 6 convex facets in longest series. Ocelli absent or indistinguishable. Frons markedly concave laterally, hence eyes appearing elevated; cuticle dull, with granule at base of each arcuate seta, granules ca. 1xef. Frontoclypeal suture arcuate, widely U-shaped. Clypeus with setae and granules similar to frons. Labrum dull, set at angle to clypeus, hidden in habitus view, apicomedially weakly emarginate. Maxillary palpi very short, combined lengths of meres much less than width of head (ratio ca. 18/42); ratios of meres 2–4 ca. 6/3/9, last mere penicillate. Mentum and submentum finely, densely punctulate, moderately setose, interstices shining.

Pronotum with anterior margin straight, median 2/5 with narrow hyaline border. Anterior angles obtuse, rather sharply rounded. Sides coarsely crenulate, rounded, widest past midlength, behind markedly attenuate, weakly emarginate. Posterior angle obtusangulate. Discal relief prominent, moderately shining, granules ca. 1xef, separated by ca. 4–6xef. Anterior and posterior impressions deep, anterior continuous with impression at each anterior angle; deep, wide impression at each posterior angle. Sculpture laterally rather densely granulate, dull.

Elytra moderately shining, sides arcuate, markedly attenuate posteriorly; margins distinct from shoulder for ca. 1/2 of length, sutural angle more acute in female than in male. Ten-seriate punctate, punctures deep and large, on disc ca. 4xef or larger, separated by less than puncture diameter; each puncture with indistinct, short, recumbent seta, no granule at base. Intervals shining, width ca. 1xpd, each with unilinear row of rather widely spaced, large, stiff, arcuate setae, larger than setae of pronotum.

Metaventrite very short, with deep, round median impression occupying posterior 1/2, strong midlongitudinal carina between anterior extreme of round impression and mesoventral intercoxal process. Metaventrite and abdominal ventrites 1–4 hydrofuge pubescent. Apical abdominal segments elongate. Ventrite 5 hydrofuge pubescent in basal 1/5, shining part sparsely pubescent in band across posterior 1/3; ventrite 6 simple, with sparse setae in posterior 1/3; last ventrite symmetrical, apex sharply rounded. Female ventrally similar to male, except apical abdominal segments not elongate, and ventrite 6 weakly apicomedially emarginate.

Legs moderately short, femora stout, tarsi very short, claws very small, combined lengths of metatibia and metatarsus about equal to width of head (ratio ca. 42/42), ratio of lengths of metatibia/metatarsus ca. 29/13. Basal 3 tarsomeres markedly setose.

Aedeagus length ca. 0.47 mm; main-piece sinuate in ventral view, markedly arcuate and abruptly widened in distal 1/ 2 in lateral view, bearing many long setae in widened portion, apex pointed ( Fig. 87). Spermatheca as illustrated ( Fig. 29).

Etymology. Named in reference to the habitat; most specimens have been collected by sifting litter in bamboo forests.

Distribution. Currently known from far eastern Congo and western Rwanda ( Fig. 103).

Notes. There are variable degrees of wing reduction in the specimens examined. In the holotype the wings have only one fold, and when unfolded are about 7/10 the length of the elytra. In examined specimens from Volcan Mikeno the wings are tiny lobes, attaining the level of the posterior border of the first or second abdominal ventrite. Specimens examined from Kivu, Uvira do not have wings. In some specimens the central impression of the metaventrite is not as distinctly steep-sided as in the holotype ( Fig. 85).