Gnathoncus brevisternus Lewis, 1907

Lackner, Tomáš, 2020, A review of Gnathoncus of Southeast Asia (Coleoptera: Histeridae: Saprininae), Acta Entomologica Musei Nationalis Pragae 60 (1), pp. 397-409 : 400-403

Gnathoncus brevisternus Lewis, 1907

( Figs 1 , 6–24 , 58)

Gnathoncus brevisternus Lewis, 1907: 321 (original description).

Gnathoncus brevisternus : BιർΚΗΑRƉτ (1916): 104 (catalogue); MΑƵUR (1984): 103 (catalogue); MΑƵUR (1997): 213 (catalogue); MΑƵUR (2004): 92 (catalogue); MΑƵUR (2011): 175 (catalogue); LΑർΚΝΕR et al. (2015): 113 (catalogue).

Type locality. China: Yunnan.

Type material examined. LΕർτοτΥΡΕ (by present designation):♁, mounted on a triangle point, left antennal club missing, left protibia missing, both metatibiae missing, ‘ Yunnan | Donckier’ [written] || ‘ Gnathoncus | brevisternus | Lewis | Type’ [written] || ‘prosternal | striae short.’ [written] || ‘George Lewis Coll. | B.M. 1926-369’ [printed] || ‘Type’ [round, redmargined, printed] || ‘D07-076’ [yellow, pencil-written] || ‘ LECTOTYPE | Gnathoncus brevisternus | Lewis, 1907 | Designated by | T. Lackner, 2008’ [red, hand-written] ( NHM). LΕඐιඌ (1907) does not specify the number of specimens in his description. Lectotype designation serves to fix the identity of the species.

Additional material examined: VIETNAM: CΑΟ BằΝǤ: Động Ngườm Ngao 3 [= Tiger Cave], N22°50′59.0″ E106°42′17.7″, 433 m, 19.x.2018, A. Faille, V. T. Tu, P. V. Phu lgt. (2 ♁♁ 5 ♀♀ in SMNS; 2 ♁♁ 3 ♀♀ in CTLA). NEPAL: BΑǤΜΑτι PඋΑοεඌΗ: Kathmandu valley, Balajv env., 11.viii.1983, 1 ♁, 3 ♀♀, Th. Deuve, M. Perrau, E. Krejčí & E. Queinnec lgt., inside an unnamed cave ( ZSM).

Redescription. Body ( Fig. 1 ): PEL: 2.00– 2.70 mm; APW: 0.60–0.90 mm; PPW: 1.00– 1.75 mm; EL: 1.30–1.80 mm; EW: 1.50–2.00 mm.

Body oval, moderately convex, slightly flattened from above, elytral humeri prominent, cuticle dark brown without metallic luster; legs, mouthparts and antennae rufous.Antennal scape ( Fig. 6 ) somewhat thickened, lower margin carinate, with few short setae; club oval ( Fig. 7 ), without visible articulation, entire surface covered with dense short setae, intermingled with sparse setae; sensory structures of antennal club organ not examined.

Mouthparts. Mandibles with rounded outer margin curved inwardly, acutely pointed, tooth on inner margin very small; labrum flattened, finely punctate, with only very shallow median excavation; labral pits very small, with one short seta in each pit; terminal segment of labial palpiger elongated, its width about one-fourth its length; mentum ( Fig. 8 ) sub-quadrate, anterior angles slightly produced, anterior margin with shallow emargination, medially with two setae, lateral margins with one row of short sparse ramose setae, disc glabrous; cardo of maxilla with few short setae on lateral margin; stipes triangular, with three short setae; terminal segment of maxillary palpiger elongated, its width about one-third its length, approximately twice as long as penultimate. Clypeus large, rectangular, rounded laterally, covered with sparse fine punctures, separated by several times their diameter; disc sparsely clothed with fine round punctures separated by several times their diameter; eyes convex, well visible from above ( Fig. 6 ).

Pronotum. Pronotal sides ( Fig. 1 ) moderately convergent anteriorly, apical angles obtuse, marginal pronotal stria thin, complete, weakened behind head; disc entirely covered with deep and round punctation, medially punctures fine, separated by several times their diameter, laterally punctation coarser and denser, punctures separated by their own diameter; scutellum very small.

Elytra. Elytral epipleuron with scattered punctures of various sizes; marginal epipleural stria doubled, weakly impressed but complete; marginal elytral stria well impressed, slightly carinate, punctate, shortly continued along elytral apex, then erased; humeral elytral stria weakly impressed on basal third; internal subhumeral stria shortly present medially; elytral disc with four dorsal elytral striae I–IV, first the longest, deeply impressed, almost reaching elytral apex, second and third striae composed of fine punctures, reaching about elytral half, fourth stria only slightly shorter than second and third, basal end of fourth elytral stria forms small hook, between that and sutural elytral stria present short characteristic hooked appendix; basal end of sutural elytral stria also with small hook; sutural elytral stria very short, present as short basal fragment, then obliterated. Approximately apical two-thirds of elytral disc covered with deep round punctures separated by about two times their diameter, apically not forming longitudinal rugae; on basal third punctures much finer and sparser, separated by several times their diameter.

Propygidium ( Fig. 9 ) covered with dense and coarse punctures separated by about their own diameter; pygidium ( Fig. 9 ) convex medially, covered with less dense elliptic punctures, separated by about two times their own diameter, apically with fine microsculpture.

Prosternum. Anterior margin of median portion ( Fig. 10 ) rounded; prosternal process flat, broad, dorsally covered with sparse punctures, laterally with microsculpture; carinal prosternal striae carinate, parallel on basal two -thirds, thence strongly convergent anteriorly, terminating in deep prosternal fovea; lateral prosternal striae very short, strongly convergent anteriorly, reaching carinal prosternal striae in middle of prosternal process.

Mesoventrite. Anterior margin ( Fig. 11 ) straight; marginal mesoventral stria well impressed, slightly carinate; mesoventral disc flat, with round punctures separated about their own to three times their diameter; meso-metaventral suture very thin, straight, anterad of it runs an undulate, inwardly bent meso-metaventral stria; intercoxal disc of metaventrite laterally and along apical margin covered with deep round punctures of various sizes. Lateral metaventral stria ( Fig. 12 ) well impressed, carinate, almost straight, almost reaching metacoxa; lateral disc of metaventrite ( Fig. 12 ) flat, covered with deep ellipsoid large punctures, becoming finer and sparser posteriorly; metepisternum ( Fig. 12 ) evenly covered with much coarser and denser punctation.

Abdomen. Intercoxal disc of first abdominal ventrite with lateral depressions, almost completely striate laterally; surface laterally and basally covered with moderate punctures, medially punctation very fine and sparse.

Legs. Protibia ( Fig. 13 ) slender, outer margin anteriorly with three small denticles, followed by four short teeth (second and third very approximate), topped by minute denticles, followed by three minute denticles, protarsal groove rather deep, protibial stria complete, median row of setae regular, dense, setae of outer row longer, irregular, protibial spur large and thick, growing out from anterior protibial margin, near tarsal insertion two prominent tarsal denticles present. Posterior surface of protibia ( Fig. 14 ) with irregular setae, posterior protibial stria complete, setose, inner row of setae double. Mesotibia ( Fig. 15 ) slender, outer margin with about five rather widely-spaced short denticles growing in size in proximal direction, setae of outer row regular, widely-spaced, growing in size in proximal direction; mesotibial spur rather short and stout. Anterior face of mesotibia near outer margin with dense row of thin denticles, anterior mesotibial stria almost complete, setae of inner margin fine, growing in size in proximal direction. Ultimate mesotarsomere about as long as two preceding; mesotarsal claws shorter than half of its length. Metatibia slenderer than mesotibia, denticles on outer margin very thin, near tarsal insertion two prominent stout denticles, anterior face of metatibia similar to that of mesotibia.

Male genitalia. Eighth sternite ( Fig. 16 ) separated medially, its apex with conspicuous velum; eighth tergite ( Fig. 17 ) apically almost straight; eighth sternite and tergite not fused laterally ( Fig. 18 ). Ninth tergite ( Figs 19–20 ) separated medially, apically with pores and pseudopores; tenth tergite ( Fig. 19 ) basally inwardly arcuate, narrowing apically. Ninth sternite (spiculum gastrale) basally shovel-like ( Figs 21–22 ), apically slightly inwardly arcuate.Aedeagus ( Figs 23–24 ) with strongly sclerotized apex of phallobase and base of fused parameres, narrowing apically, bluntly pointed, parameres fused in their basal two-thirds.

Differential diagnosis. This species is most similar to the widely distributed species G. rotundatus , from which it differs in larger and conspicuous prosternal fovea, wider prosternum, and carinate carinal prosternal striae. The aedeagi of the two species are likewise similar; however, that of G. brevisternus is strongly narrowed towards apex while that of G. rotundatus is blunt apically (compare Figs. 23 and 41 ).

Biology. Vietnamese and Nepali specimens were found inside caves by speleo-entomologists. Presumably this species feeds on arthropod larvae occurring on (bat) guano.

Distribution. China: Yunnan; newly reported from Vietnam and Nepal.

Figures

Figs 1–5. Dorsal (1–4) and ventral (5) habitus of SE Asian Gnathoncus species. 1 – G. brevisternus Lewis, 1907; 2 – G. nannetensis (Marseul, 1862); 3 – G. rotundatus (Kugelann, 1792); 4–5 – G. sechuanus sp. nov.

Figs 6–15. Gnathoncus brevisternus Lewis, 1907, SEM micrographs. 6 – head, dorsal view; 7 – antennal club, ventral view; 8 – mentum; 9 – propygidium and pygidium; 10 – prosternum; 11 – mesoventrite; 12 – lateral disc of metaventrite and metepisternum; 13–14 – protibia (13 – dorsal view; 14 – ventral view); 15 – mesotibia, dorsal view.

Figs 16–51. Male genitalia of SE Asian Gnathoncus species. 16–24 – G. brevisternus Lewis, 1907: 16–18 – VIII sternite and tergite (16 – ventral view; 17 – dorsal view; 18 – lateral view). 19–20 – IX and X tergites (19 – dorsal view; 20 –lateral view). 21–22 – IX sternite (spiculum gastrale) (21 – ventral view; 22 – lateral view). 23–24 – aedeagus (23 – dorsal view; 24 – lateral view). 25–34 – G. nannetensis (Marseul, 1862) (after ÔΗΑRΑ 1994). 25–27 – VIII sternite and tergite (25 – apical half in ventral view; 26 – dorsal view; 27 – lateral view).28–30 – aedeagus (28 – apex, apical view; 29 – dorsal view; 30 – lateral view). 31–32 – IX and X tergite (31 – dorsal view; 32 – lateral view). 33–34 – IX sternite (spiculum gastrale) (33 – ventral view; 34 –lateral view). 35–42 – G. rotundatus (Kugelann, 1792) (after ÔΗΑRΑ 1994). 35–37 – VIII sternite and tergite (35 – apical half in ventral view; 36 – dorsal view; 37 – lateral view). 38–39 – IX and X tergite (38 – dorsal view; 39 – lateral view). 40 – IX sternite (spiculum gastrale), ventral view. 41–42 – aedeagus (41 – dorsal view; 42 – lateral view). 43–51 – G. sechuanus sp. nov. 43–45 – VIII sternite and tergite (43 – ventral view; 44 – dorsal view; 45 – lateral view). 46–47 – IX and X tergites (46 – dorsal view; 47 –lateral view). 48–49 – IX sternite (spiculum gastrale) (48 – ventral view; 49 – lateral view). 50–51 – aedeagus (51 – dorsal view; 51 – lateral view)