A revision of the Stenus flammeus group (Coleoptera, Staphylinidae) with descriptions of twelve new species

Abstract The Stenus flammeus group is proposed and twelve new species of the group are described: Stenus corniculus sp. n., Stenus daicongchaoi sp. n., Stenus jiajinshanus sp. n., Stenus jindingianus sp. n., Stenus paraflammeus sp. n., Stenus pengzhongi sp. n., Stenus pseudoflammeus sp. n., Stenus punctidorsus sp. n., Stenus tuyueyei sp. n., Stenus xilingmontis sp. n., and Stenus zhoudeyaoi sp. n. from Sichuan Province, and Stenus dabashanus sp. n. from Shaanxi Province. Their diagnostic characters are illustrated and a key to species of the group is provided.


Introduction
The Stenus flammeus complex consisting of S. flammeus Puthz, 2008 andS. bostrychus Tang &Puthz, 2008 (both see Tang, Zhao & Puthz, 2008) was established by Tang, Zhao & Puthz in 2008 and it was assigned to the Stenus cirrus group at that time. With more material collected and in-depth understanding of the Chinese fauna of the genus Stenus increasing, it is clarified now that S. flammeus and its affinis represent a separate species group which may not be closely related to the Stenus cirrus group. The distributional range of the Stenus flammeus group is known only from the Sichuan Basin, while the range of the Stenus cirrus group is much larger, covering the most central area of East Asia from Vietnam (Puthz 1981), Hainan (Puthz 2003) and Taiwan (Puthz 2009) to Shaanxi (Tang et al. 2005) and Japan (Naomi 2004). Although a unique character in the genus, bearing long suberect setae on the abdomen, is shared by both groups, the members of the Stenus flammeus group differ from those of the Stenus cirrus group by the following characters: paraglossa coniform, while they are oval in the Stenus cirrus group; male sternite IX with apicolateral projections relatively long and posterior margin usually with median projection (exceptions: S. xilingmontis, S. dabashanus, S. jiajinshanus, S. zhoudeyaoi), while in the Stenus cirrus group, male sternite IX with apicolateral projections relatively short and posterior margin almost without median projection; spermatheca weakly sclerotized or even difficult to be observed although basal porch and/or basal duct are usually strongly sclerotized, while in the Stenus cirrus group, the entire spermatheca is always sclerotized in mature females.

Material and methods
The specimens examined in this paper were collected by sifting leaf litters in forests and killed with ethyl acetate. For examination of the genitalia, the last three abdominal segments were detached from the body after softening in hot water. The aedeagi or the spermathecae, together with other dissected pieces, were mounted in Euparal (Chroma Gesellschaft Schmidt, Koengen, Germany) on plastic slides. Photos of sexual characters were taken with a Canon G9 camera attached to an Olympus SZX 16 stereoscope; habitus photos were taken with a Canon macro photo lens MP-E 65 mm attached to a Canon EOS 7D camera and stacked with Zerene Stacker (http://www.zerenesystems.com/cms/stacker).
The type specimens treated in this study are deposited in the following public and private collections: Description. Brachypterous; Head black, other body parts dark brown, each elytron with a large orange spot, which is about 3/5 as long as and 1/2 as broad as the respective elytron. Antennae yellowish brown, club infuscate, maxillary palpi and legs yellowish brown.
BL: 3.1-3.4mm, FL: 1.5-1.6 mm. Head 1.25-1.31 times as wide as elytra; interocular area with two deep longitudinal furrows, median portion convex, slightly extending beyond the level of inner eye margins; punctures round, mostly well delimited, slightly larger and sparser on median area than those near inner margins of eyes, diameter of large punctures about as wide as apical cross section of antennal segment II; interstices smooth, narrower than half to entire diameter of punctures except those along the midline of the convex median portion, which may be twice as wide as diameter of punctures. Paraglossa coniform.
Pronotum 1.05-1.08 times as long as wide; disk slightly uneven, with distinct median longitudinal furrow, which is about 3/5 as long as pronotum; punctures more or less confluent, slightly larger than those of head; interstices smooth, distinctly narrower than half the diameter of punctures except those at the actual middle of longitudinal furrow, which could be three times as wide as diameter of punctures.
Elytra 0.95-0.98 times as long as wide; disk relatively even; punctures more or less longitudinally confluent, slightly larger than those of pronotum; interstices smooth, distinctly narrower than half the diameter of punctures.
Legs with tarsomeres IV deeply bilobed. Abdomen cylindrical; line-like paratergites present only in segment III, tergites and sternites totally fused in segment IV-VI, tergite VII without apical membra-nous fringe; punctures mostly round, becoming slightly smaller posteriad; interstices smooth, mostly narrower than diameter of punctures.
Remarks. The species can be distinguished from other related species by the following characters: body size smaller, surfaces of pronotum and elytra rather even and ratio of HW/EW larger.
Etymology. This species is named in honor of Mr. Zhong Peng who collected some specimens of the new species. Head 1.03-1.07 times as wide as elytra, interocular area with two deep longitudinal furrows, median portion convex, slightly extending beyond the level of inner eye margins; punctures round, slightly confluent, slightly larger and sparser on median area than those near inner margins of eyes, diameter of large punctures about as wide as apical cross section of antennal segment II; interstices smooth, much narrower than half the diameter of punctures except those along the midline of the convex median portion, which may be twice as wide as diameter of punctures. Paraglossa coniform.
Pronotum 0.91-0.95 times as long as wide, disk uneven, with broad median longitudinal furrow throughout, two shallow impressions in anterior half, two shallow impressions in about middle, two shallow impressions in posterior half; punctures confluent, of similar size to those of head; interstices smooth, narrower than half the diameter of punctures except those at the bottom of longitudinal furrow, which could be much larger.
Elytra 0.82-0.90 times as long as wide; disk moderately even with indistinct longitudinal humeral impression, indistinct postero-lateral impression and indistinct long sutural impression, suture moderately convex; punctation strongly and longitudinally confluent; interstices smooth, very narrow and ridge-like.
Legs with tarsomeres IV deeply bilobed. Abdomen cylindrical; paratergites very narrow and punctate, present only in segment III, tergites and sternites totally fused in segment IV-VI, tergite VII without apical membranous fringe; punctures gradually becoming smaller posteriad, punctures of abdominal tergites III slightly larger than those of pronotum in average; interstices smooth except sometimes traces of reticulation presented at last three tergites, narrower than the diameter of punctures on tergites III-VI.
Remarks. The species can be distinguished from other related species except S. corniculus sp. n. by smaller body size and longitudinally confluent punctation of elytra. To distinguish from S. corniculus sp. n., see diagnoses of the latter.
Etymology. The specific name is derived from the type locality of this species. Similar to S. jindingianus sp. n. in most aspects, but differs in the following characters: Head with interocular area entirely black; the traces of elytral marks more distinct and larger; abdominal tergites with punctures relatively sparser especially those of posterior area of each tergite.
Male. Sternite VII (Fig. 24) impressed at posteromedian part delimited by edged ridge on each side, posterior margin of the impression emarginated with a sharp projection on each side; sternite VIII ( Fig. 25) with triangular emargination at middle of posterior margin; sternite IX ( Fig. 26) with long apicolateral projections, posterior margin with broad and shallow median projection. Aedeagus (Figs 28, 29) slender; with median lobe broadest at about basal 2/5 and gradually tapering apicad, apical sclerotized area with an apical cuspidate projection; expulsion clasps large; parameres distinctly shorter than median lobe, slightly swollen at apical parts, each with 9-11 setae on apico-internal margins. Distribution. China (Sichuan). Remarks. The species resembles Stenus jindingianus sp. n. in most aspects, the main differences between them appear in proportions of pronotum and elytra.
Etymology. The specific name is a combination of the Latin words "cornic" and "ulus" after its sternite VII decorated by sharp projections. Description. Brachypterous; body brownish except head with interocular area somewhat darker and elytra lighter, each elytron with slender spot, which is about 1/2 as long as and 1/3 as broad as the respective elytron, sometimes they are inconspicuous. Antennae, maxillary palpi and legs yellowish brown except antennal club infuscate.

Stenus daicongchaoi
BL Head 1.06-1.08 times as wide as elytra; interocular area with two deep longitudinal furrows, median portion convex, reaching the level of inner eye margins; punctures round, partly confluent, slightly larger and sparser on median area than those near inner margins of eyes, diameter of large punctures about as wide as apical cross section of antennal segment II; interstices smooth, much narrower than half the diameter of punctures except those along the midline of the convex median portion, which may be twice as wide as the diameter of punctures. Paraglossa coniform.
Pronotum 1.04-1.07 times as long as wide; disk uneven, with distinct median longitudinal furrow, two impressions in anterior half, transverse impression in the middle, and two impressions in posterior half; punctures more or less confluent, of similar size to those of head; interstices partially and indistinctly reticulated, more or less narrower than half the diameter of punctures except those at the bottom of longitudinal furrow, which could be larger.
Legs with tarsomeres IV deeply bilobed. Abdomen cylindrical; paratergites very narrow and punctate, present only in segment III, tergites and sternites totally fused in segment IV-VI, tergite VII without apical membranous fringe; punctures round, becoming slightly smaller posteriad; interstices smooth except those of last two tergites shallowly reticulated, narrower than half the diameter of punctures on tergite III-VI.
Distribution. China (Sichuan). Remarks. The species is similar to S. bostrychus, but can be distinguished from the latter by less confluent punctation of pronotum and relatively larger punctures of abdomen.
Etymology. This species is named in honor of Mr. Cong-Chao Dai who collected some specimens of the new species. Description. Brachypterous; Body reddish brown except head with interocular area blackish, each elytron with a very vague and inconspicuous small spot. Antennae, maxillary palpi and legs yellowish brown except antennal club infuscate. Head 1.13-1.15 times as wide as elytra, interocular area with two deep longitudinal furrows, median portion convex, slightly extending beyond the level of inner eye margins; punctures round, more or less confluent, almost the same size, diameter of punctures about as wide as apical cross section of antennal segment II; interstices smooth, much narrower than half the diameter of punctures except those along the midline of the convex median portion, which may be slightly narrower than diameter of punctures. Paraglossa coniform.
Pronotum 1.02-1.05 times as long as wide; disk uneven, with broad median longitudinal furrow throughout, two impressions in anterior half each with an small outer tubercle, two impressions in about middle each with an inner tubercle, two deep impressions in posterior half each with an larger outer tubercle; punctures confluent, slightly smaller than those of head; interstices smooth, narrower than half the diameter of punctures except those at the bottom of longitudinal furrow, which could be much larger.
Elytra 0.92-0.94 times as long as wide; disk moderately uneven with distinct longitudinal humeral impression, distinct postero-lateral impression and long sutural impression, suture moderately convex; punctation and interstices similar to those of pronotum, except punctures slightly larger.
Legs with tarsomeres IV deeply bilobed. Abdomen cylindrical; paratergites very narrow and punctate, present only in segment III, tergites and sternites totally fused in segment IV-VI, tergite VII without apical membranous fringe; punctures round, becoming slightly smaller posteriad; interstices smooth, narrower than half the diameter of punctures on tergite III-VI.

Distribution. China (Sichuan).
Remarks. The new species is characterized by large and dense punctation of entire body especially of abdominal tergites.
Etymology. The specific name is derived from the dense punctation of abdominal tergites. of inner eye margins; punctures round, well delimited on the posterior areas of furrows and distinctly confluent on the rest parts especially on median portion, diameter of large punctures about as wide as medial cross section of 2nd antennal segment; interstices between punctures smooth, distinctly narrower than half the diameter of punctures. Paraglossa coniform.

Stenus paraflammeus
Pronotum 0.90-0.96 times as long as wide; disk conspicuously uneven, with broad and deep median longitudinal furrow which begins from the anterior margin and ends at about basal 1/5, two deep impressions in anterior half each with an outer tubercle, two distinct impressions in about middle each with an inner tubercle, two deep impressions in posterior half each with an outer tubercle; punctures round and strongly confluent, mostly slightly smaller than those on frons; interstices smooth, much narrower than half the diameter of punctures except in median furrow, which is partially reticulated and broadly impunctate.
Elytra 0.85-0.89 times as long as wide; disk uneven with deep humeral impression, distinct postero-lateral impression and deep sutural impression, median portion between humeral impression and sutural impression distinctly convex; punctation irregular, punctures confluent, slightly larger than those on pronotum; interstices smooth, much narrower than half the diameter of punctures.
Legs with tarsomeres IV strongly bilobed. Abdomen cylindrical; paratergites very narrow and punctate, present only in segment III, tergites and sternites totally fused in segment IV-VI, tergite VII without apical membranous fringe; punctures mostly round, becoming slightly smaller posteriad; interstices smooth on the basal four tergites and more or less sculptured on the rest tergites, narrower than half the diameter of punctures on basal three tergites and narrower than diameter of punctures on the following two tergites.

Distribution. China (Sichuan).
Remarks. This new species is closely related to S. flammeus and S. pseudoflammeus, but can be easily distinguished from the latter two species by its broader pronotum.
Etymology. The specific name is derived from the similar appearance of Stenus flammeus. Similar to S. paraflammeus sp. n. in most aspects, but differs in the following characters: the convex median portion of head extending to the same level of inner eye margins; punctures of forebody relatively smaller, larger punctures on head about as wide as basal cross section of 2nd antennal segment; impressions of pronotum and elytra shallower; punctation of abdominal tergites slightly finer and sparser.
Distribution. China (Sichuan). Remarks. The species is similar to S. paraflammeus but can be distinguished from the latter by slender pronotum; and it is also very similar to S. flammeus, dissections are necessary to distinguish them.
Etymology. The specific name is derived from the similar appearance of Stenus flammeus.  Head 1.06-1.09 times as wide as elytra; interocular area with two deep longitudinal furrows, median portion convex, slightly extending beyond the level of inner eye margins; punctures round, slightly larger and sparser on median area than those near inner margins of eyes, diameter of large punctures about as wide as apical cross section of antennal segment II; interstices smooth, much narrower than half the diameter of punctures except those along the midline of the convex median portion, which may be 1.5 times as wide as diameter of punctures. Paraglossa coniform.

Stenus xilingmontis
Pronotum 0.95-1.00 times as long as wide; disk uneven, with distinct median longitudinal furrow, two impressions in anterior half, transverse impression in the middle, and two impressions in posterior half; punctures partially confluent, of similar size to those of head; interstices smooth except few reticulations at the bottom of median furrow, more or less narrower than half the diameter of punctures except those at the bottom of longitudinal furrow, which may be twice as wide as diameter of punctures.
Elytra 0.89-0.93 times as long as wide; disk moderately uneven with distinct longitudinal humeral impression, distinct postero-lateral impression and long sutural impression, suture moderately convex; punctation and interstices similar to those of pronotum except punctures slightly confluent longitudinally.
Legs with tarsomeres IV deeply bilobed. Abdomen cylindrical; paratergites very narrow and punctate, present only in segment III, tergites and sternites totally fused in segment IV-VI, tergite VII without apical membranous fringe; punctures of abdominal tergites III-VIII round, gradually becoming smaller posteriad; interstices smooth except those of last three tergites more or less shallowly reticulated, narrower than half the diameter of to the diameter of punctures.

Remarks.
The new species shares the same appearance with S. zhoudeyaoi sp. n., and both of them distributed on the same mountain. Dissections are necessary to distinguish them, though the altitude information will be also helpful.
Etymology. The specific name is derived from the type locality of this species. Similar to S. xilingmontis sp. n. in most aspects, but differs in the following characters: Body coloration darker; punctation of pronotum and elytra less confluent. Sexual characters are also similar to S. xilingmontis sp. n. except the aedeagus and spermatheca. Aedeagus (Figs 61, 62) with apical sclerotized area larger and expulsion clasps smaller; Head 1.15-1.19 times as wide as elytra, interocular area with two deep longitudinal furrows, median portion convex, distinctly extending beyond the level of inner eye margins; punctures round, mostly well delimited, slightly larger and sparser on median area than those near inner margins of eyes, diameter of large punctures about as wide as apical cross section of antennal segment II; interstices smooth, much narrower than half the diameter of punctures except those along the midline of the convex median portion, which may be as wide as diameter of punctures. Paraglossa coniform.

Stenus zhoudeyaoi
Pronotum 0.98 times as long as wide, disk uneven, with distinct median longitudinal furrow, two impressions in anterior half, transverse impression in the middle, and two impressions in posterior half; punctures slightly confluent, of similar size to those of head; interstices smooth, more or less narrower than half the diameter of punctures except those at the bottom of longitudinal furrow, which could be larger.
Elytra 0.85-0.86 times as long as wide; disk moderately uneven with shallow longitudinal humeral impression, distinct postero-lateral impression and long sutural impression, suture moderately convex; punctures more or less longitudinally confluent, slightly larger than those of pronotum; interstices smooth, distinctly narrower than half the diameter of punctures.
Legs with tarsomeres IV deeply bilobed. Abdomen cylindrical; line-like paratergites present only in segment III, tergites and sternites totally fused in segment IV-VI, tergite VII without apical membranous fringe; punctures of abdominal tergites III-VIII round to elliptic, gradually becoming smaller posteriad; interstices smooth except those of last two tergites shallowly reticulated, narrower than half the diameter of punctures.

Remarks.
To distinguish the new species from other species with small body length, see characters listed in key.
Etymology. The specific name is derived from the type locality of this species. Head 1.14 times as wide as elytra; interocular area with two deep longitudinal furrows, median portion convex, reaching the level of inner eye margins; punctures round, slightly larger on posterior areas of furrows than those on rest areas, diameter of large punctures about as wide as basal cross section of antennal segment II; interstices smooth, much narrower than half the diameter of punctures except those along the midline of the convex median portion, which may be as wide as diameter of punctures. Paraglossa coniform.
Pronotum as long as wide; disk uneven, with distinct median longitudinal furrow, two impressions in anterior half, transverse impression in the middle, and two impressions in posterior half; punctures more or less confluent, of similar size to those of head; interstices faintly reticulated, more or less narrower than half the diameter of punctures except those at the bottom of longitudinal furrow, which could be three times as wide as diameter of punctures.
Elytra 0.95 times as long as wide; disk relatively uneven with shallow longitudinal humeral impression, distinct postero-lateral impression and long sutural impression, suture moderately convex; punctation and interstices similar to those of pronotum.
Legs with tarsomeres IV deeply bilobed. Abdomen cylindrical; distinct paratergites absent, rudimentary lateral border present only on anterior half of segment III, tergites and sternites totally fused in posterior half of segment III and entire segment IV-VI; posterior margin of tergite VII without membranous fringe; punctures mostly round, becoming slightly smaller posteriad; interstices smooth except those of last three tergites shallowly reticulated, larger to much larger than diameter of punctures except those on basal impressions of basal three abdominal tergites, which could be narrower than half the diameter of punctures.
Male. Sternite VIII (Fig. 68) with triangular emargination at middle of posterior margin; sternite IX ( Fig. 69) with very long apicolateral projections, posterior margin with long and sharp median projection. Aedeagus (Figs 70, 71) robust; apical sclerotized area very wide and short with small and round tip; expulsion clasps large; parameres a little shorter than median lobe, slightly swollen in apical part, with 12 setae on apico-internal margins. Description. Brachypterous; body reddish brown except interocular area of head and abdominal segments VIII-X blackish. Antennae, maxillary palpi and legs yellowish brown except antennal club infuscate.
Head 1.15-1.21 times as wide as elytra, interocular area with two deep longitudinal furrows, median portion convex, extending beneath the level of inner eye margins; punctures round, mostly well delimited, slightly larger and sparser on median area than those near inner margins of eyes, diameter of large punctures about as wide as basal cross section of antennal segment II; interstices faintly reticulated, much narrower than half the diameter of punctures except those along the midline of the convex median portion, which may be twice as wide as diameter of punctures. Paraglossa coniform.
Pronotum 0.96-1.05 times as long as wide; disk uneven, with median longitudinal furrow throughout; punctures confluent, of similar size to large punctures of head; interstices reticulated, narrower than half the diameter of punctures everywhere.
Elytra 0.83-0.93 times as long as wide, disk moderately uneven with distinct longitudinal humeral impression, distinct postero-lateral impression and long sutural impression, suture moderately convex; punctures longitudinally confluent and slightly larger than those of pronotum; interstices faintly reticulated, narrower than half the diameter of punctures.
Legs with hind tarsi 0.73 times as long as hind tibiae, tarsomeres IV deeply bilobed. Abdomen cylindrical; line-like paratergites present only in segment III, tergites and sternites totally fused in segment IV-VI, tergite VII without apical membranous fringe; punctures distinctly smaller than those of elytra, gradually becoming smaller posteriad; interstices smooth, wider than the diameter of punctures except some on tergites III and IV, which could be smaller.
Female. Sternite VIII slightly prominent at middle of posterior margin; spermatheca (Fig. 74) weekly sclerotized, basal porch large and spermathecal duct with multiple bends.
Remarks. The species can be easily recognized by distinctly darkened abdominal tip and reticulated forebody.
Etymology. The specific name is derived from the type locality of this species.