Bull. Natl. Mus. Nat. Sci., Ser. A, 41(1), pp. 55–62, February 20, 2015

Two New Species of the Genus Stenus Latreille (Coleoptera, Staphylinidae),with the First Record and Redescription of S. bifoveolatus Gyllenhal
from Japan
Shun-Ichiro Naomi1 and Shûhei Nomura2
1
Natural History Museum and Institute, Chiba,
955–2 Aoba-cho, Chuo-ku, Chiba 260–8682, Japan
E-mail: naostenus@hb.tp1.jp
2
National Museum of Nature and Science,
4–1–1 Amakubo, Tsukuba, Ibaraki 305–0005, Japan
E-mail: nomura@kahaku.go.jp(Received 9 December 2014; accepted 24 December 2014)

Abstract This is the 48th taxonomic study on the subfamily Steninae (Coleoptera, Staphylinidae) from Japan, with descriptions of 2 new species of the genus Stenus Latreille, and detailed
illustrations of the taxonomically important characters including abdominal terminalia, aedeagus,
endophallic structures and spermatheca. The new species of Stenus described herein are as follows: S. aboblitus (Hokkaido, Aomori, Fukushima, Tochigi, Tokyo and Chiba Prefs.) and S. vernicosus (Tottori Pref.). In addition, Stenus bifoveolatus Gyllenhal, 1827 is ﬁrst recorded fromJapan (Hokkaido); and it is redescribed and illustrated.
Key words : Coleoptera, Staphylinidae, Stenus, new species, new record, Japan.

Introduction

Stenus aboblitus sp. nov.

At present, the rove beetle genus Stenus (Coleoptera, Staphylinidae, Steninae) of Japan consistsof 249 species and 8 subspecies (Naomi andPuthz, 2013). During the course of present study,
we discovered 2 additional new species of Stenus
from Hokkaido and Honshu, Japan. Thus we are
to describe and illustrate them in this paper. The
holotypes of the new Stenus species describedare deposited in the National Museum of Natureand Science, Tsukuba (abbreviated as NMNS);
and the paratypes are in Naomi Collection unlessotherwise noted. In addition, we ﬁrst record S.
bifoveolatus Gyllenhal, 1827 from Japan, with its
redescription and illustration of the taxonomic
characters.

[New Japanese name: Hoso-ginge-medaka-hanekakushi](Fig. 1)
Stenus puberulus (not of Sharp, 1874): Puthz, 2012: 93(see also p. 97, ﬁgs. 25–26). (Partim.)

Male and female. Macropterous species;
body 2.7–3.0 mm in length, perfectly covered
with short and silvery setae which arise frompunctures. Body (including mouthparts and legs)
entirely black and weakly shining, but antennae
with basal segments piceous, lustrous, and apicalsegments dark red. Head with a pair of longitudinal depressions running in parallel, median longitudinal area between the depressions narrow;
punctures round to elliptical, distinct, dense. Pronotum with punctures very dense, distinct, round,regular, without median longitudinal depression.
Elytra similarly punctate as on pronotum, butpunctures a little larger than those on pronotum.

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Shun-Ichiro Naomi and Shûhei Nomura

Fig. 1. Stenus aboblitus sp. nov. (A–C, E–F: Okuyagen; D: Hakken-zan). A, Gonocoxite; B, aedeagus of ventralview; C, 9th and 10th terga of male; D, 8th venter of male; E, 9th venter of male; F, 9th and 10th terga offemale. Scale 1: 0.2 mm for B–F and 0.1 mm for A.

Abdomen with distinct paratergites; punctures
dense, distinct and round in anterior segments,small and regular in posterior segments.
Male. Body elongate, subcylindrical; 7thventer posteromedially with a lustrous and semicircular ﬂat area, the ﬂat area very shallowly
emarginate; 8th venter (Fig. 1D) posteromediallywith a broad emargination; 9th tergum (Fig. 1C)
with ventral apophyses rather short, thin; 9thventer (Fig. 1E) minutely serrate between apicolateral teeth, with the apicolateral teeth short,pointed; 10th tergum entire or very weakly emarginate (Fig. 1C). Aedeagus (Fig. 1B) with median
lobe narrow in apical half, weakly bulbous in

New Stenus species from Japan

basal half, gently rounded at apicolateral corners;
apical sclerotized area long, acutely pointed posteromedially, with anterior margin arcuate. Endophallus with median longitudinal bands (Fig. 1B)very long, narrow, almost running in parallel;
expulsion clasps (Fig. 1B) large, anterior plates
completely connate to form a half longitudinal
section of short duct, posterior plate baculiform,slender; basal tube (Fig. 1B) entirely membranous, with basal room large, elongate-ovoidal,
tube body short, weakly swollen in the middle.
Parameres (Fig. 1B) slightly incurved, thick,rather short, not reaching the apex of median
lobe, obliquely truncate apically to form apicalpart of paramere which is very short, with morethan 17 short setae.
Female. Body subcylindrical, with abdomen
more or less impressed dorsally. Eighth venter
gently rounded at posterior margin; 9th tergum(Fig. 1F) without ventral apophyses; gonocoxites(Fig. 1A) each almost truncate posteriorly, irregularly serrate at posterior margin, weakly produced apicomesially, with a tuft of very long,straight setae; 10th tergum (Fig. 1F) entire.
Type series. Holotype (No. NSMT-I-C-200255
in NMNS): ♂, Okuyagen, Shimokita Peninsula,Aomori Pref., 2. viii. 1987, S. Nomura leg. Paratypes (Nos. NSMT-I-C-200256–200257 inNMNS): 1 ♂, Ikushina River, Ikushina, Sharicho, Hokkaido, 11. vi. 2014, T. Kato leg. (ItoCol.); 1 ♂1 ♀, Mt. Hakken-zan, Hokkaido, 27.
v. 1997, N. Nishikawa leg.; 1 ♂, Misumai, Sapporo, Hokkaido, 7. vii. 1977, S. Naomi leg.;2 ♂3 ♀, same data as holotype; 1 ♂, YugawaRiver, Wakamatsu, Fukushima Pref., 1. viii.
1948, Y. K. leg. (NMNS); 1 ♂, Shiobara, Tochigi
Pref., 22. viii. 1976, T. Niisato leg.; 1 ♂, Ohme,Tokyo-to, 19. viii. 1976, Y. Kurosawa leg.
(NMNS); 2 ♂, Yoro Valley, Ichihara, Chiba
Pref., 9. v. 1993, K. Ohgi leg.
Distribution. Japan (Hokkaido; Honshu:
Aomori, Fukushima, Tochigi, Tokyo and Chiba
Prefs.).
Remarks. Stenus aboblitus sp. nov. belongs
to the species group of S. incanus Erichson. This
new species is closely allied to S. puberulus

57

Sharp, 1874, but it is clearly distinguishable fromthe latter by the following combination of characters: the undersides of femora are darker incoloration (while they are reddish brown to dark
reddish brown in S. puberulus); the punctures on
the abdomen are a little larger and denser; theaedeagus is distinctly narrower, and in generalmore acutely pointed apically (Fig. 1B); the parameres are shorter and do not reach the apex ofmedian lobe (Fig. 1B); the fused anterior plate ofexpulsion clasp of endophallus is narrower (Fig.
1B); and the rod-like posterior plate of expulsion
clasp is a little longer and less curved mesially(Fig. 1B).
Etymology. The speciﬁc epithet of this newspecies consists of the Latin sufﬁx “ab-” (whichmeans “apart from”) and the name of a Stenus
species “oblitus”. We wish to name this new species S. aboblitus in the following reason: Both S.
oblitus Sharp, 1874 and S. aboblitus inhabit theplains and low mountainous regions in Kanto
district, and have similar small sizes. During theﬁeld surveys, entomologists think they collectsuch beetles as S. oblitus but sometimes notice it
is not so when examining it under the binocular
but S. aboblitus.
Stenus bifoveolatus Gyllenhal, 1827
[New Japanese name: Kita-ashibe-medaka-hanekakushi](Fig. 2)
Stenus bifoveolatus Gyllenhal, 1827: 500; Herman, 2001:2083.

Male and female. Macropterous species;
body 2.8–3.1 mm in length, moderately shining.
Body and labrum black; antennae yellow to yellowish brown except for 1st segments which areblack; maxillary palpi yellow; legs with dorsal
sides black, ventral sides red to dark red. Headhardly concave dorsally, with the central part ofvertex a little higher than eyes, and with a pair ofshallow, longitudinal depressions between eyes;
punctures round, distinct, dense and regular. Pronotum a little broader than long, weakly unevenlaterally, without median longitudinal depres-58

Shun-Ichiro Naomi and Shûhei NomuraFig. 2. Stenus bifoveolatus Gyllenhal, 1827. (A, E–F: Akan; B, D, I: Furuume; C, G–H: Tokachi). A, Aedeagusof ventral view; B, 9th and 10th terga of female; C, apical part of 8th venter of male; D, apical part of 8th venter of female; E, right elytron; F, endophallus; G, 9th venter of male; H, 9th and 10th terga of male; I, posterior
part of gonocoxite. Scale 1: 0.2 mm for A–D, G–I and 0.1 mm for F and scale 2: 0.3 mm for E.

New Stenus species from Japansion; punctures dense, distinct, round and regular. Elytra slightly uneven laterally, similarly
punctate as on pronotum, but punctures a littlelarger than those on pronotum (Fig. 2E). Abdomen with narrow paratergites in 3rd to 6th segments; punctures moderately dense to dense, distinct and round in anterior segments, very small
to small, sparse and regular in posterior segments.
Male. Sixth venter posteromedially with ashallow, narrow and semicircular depression, thedepressed area shallowly emarginate; 7th venter
medially with an elongate-elliptical depression,
which does not reach the posterior margin; 8thventer (Fig. 2C) posteromedially with a large,broad emargination; 9th tergum (Fig. 2H) withventral apophyses long; 9th venter (Fig. 2G)
broad, rounded apicolaterally, substraight andminutely serrate at posterior margin; 10th tergum(Fig. 2H) entire. Aedeagus (Fig. 2A) with median
lobe well-pigmented, weakly bulbous in basalpart, narrowed posteriorly, gently rounded at apicolateral corners, and acutely pointed apically;
apical sclerotized area very long (5/12 times aslong as median lobe), weakly produced anteromedially. Endophallus with median longitudinalbands (Fig. 2F) each very broad, folded to a different direction so that each forms a V-shaped
band when seen ventrally; expulsion clasps (Fig.
2F) small, separated, anterior plate completelyfused with posterior plate; basal tube located in
the sclerotized inner sac (Fig. 2F), with basal
room weakly bulbous, tube body simple, straight,
pointed. Parameres (Fig. 2A) substraight, extending posteriorly a little before the apex of median
lobe, apical part of paramere moderately swollen
mesially, relatively short, with about 30 setae ofvarious length.
Female. Eighth venter (Fig. 2D) obtusely
pointed at posteromedian part; 9th tergum (Fig.
2B) without ventral apophyses; gonocoxites (Fig.
2I) each partially cut longitudinally at the mesial
side to form a separated ﬂap, each gonocoxite
rounded apically, minutely serrate at posterior
margin, and apicolaterally with a tuft of longsetae; 10th tergum (Fig. 2B) entire.

59

Specimens examined. 1 ♂(NMNS): Mitsumata, Kami-shihoro, Tokachi, Hokkaido, 22. vii.
1984, M. Tomokuni leg.; 1 ♂, Akan, Hokkaido,
16. vi. 1976, M. Sato leg.; 1 ♀, Furuume,Bihoro-cho, Hokkaido, 27. viii. 1993, T. Katoleg.
Distribution. Europe, Caucasus, Russia,Kurile and Japan (Hokkaido).
Remarks. This is the ﬁrst record of Stenus
bifoveolatus Gyllenhal, 1827 (the species groupof S. pallitarsis Stephens) from Japan. S. bifoveolatus is closely allied to S. latitarsis Sharp, 1889
from Japan and S. exter Puthz, 2006 from Taiwan, but it is clearly distinguishable from the latter by the following characters: the body is a little smaller; the punctures on the anterior
segments of abdomen are a little larger; theaedeagus is distinctly narrower in posterior part,and more acutely pointed apically (Fig. 2A), theparameres are shorter and do not reach the apexof median lobe (Fig. 2A), and the endophallus(Fig. 2F) is differently structured as describedabove.
Stenus vernicosus sp. nov.
[New Japanese name: Tsuya-tachige-medaka-hanekakushi](Fig. 3)

Male and female. Brachypterous species;
body 4.0–4.3 mm in length, glossy, with head andabdomen strongly glittering, sparsely covered
with thin, suberect setae; antennae very slender,
long, with sparse long setae. Body and labrum
black; antennae with basal segments clear yellowish brown, apical segments brown to darkbrown; maxillary palpi and legs yellowish brown
to reddish brown. Head moderately concave
between eyes, vertex narrow, with a pair of longitudinal depressions; punctures round to elliptical, various in size, setiferous, distinct and dense.
Pronotum weakly uneven, without median longitudinal depression; punctures very dense, relatively small, distinct and round. Elytra uneven,with punctures round, rough, a little larger thanthose on pronotum. Abdomen weakly narrowed60

Shun-Ichiro Naomi and Shûhei Nomura

Fig. 3. Stenus vernicosus sp. nov. (A–E: Daisen; F–G: Kenashi). A, Ninth venter of male; B, posterior part ofaedeagus of ventral view; C, 9th and 10th terga of male; D, apical part of median lobe with inverted endophallic structure; E, apical part of 8th venter of male; F, spermatheca; G, apical part of gonocoxite. Scale: 0.2 mmfor A–E and 0.1 mm for F–G.

New Stenus species from Japan

posteriorly; paratergites each with a few setiferous punctures in 3rd to 5th segments, but in 5thsegment, paratergites each very narrow, narrowed posteriorly; punctures on anterior parts of
3rd and 4th segments large, elliptical, distinct,
dense to very dense, those on posterior parts of
3rd and 4th segments small, sparse, those on posterior segments very small, very sparse.
Male. Eighth venter (Fig. 3E) posteromedially with a broad emargination; 9th tergum (Fig.
3C) with ventral apophyses long, thin, straight;
9th venter (Fig. 3A) almost straight between apicolateral teeth, with the apicolateral teeth short,pointed, and with very long setae on posterior
part of 9th venter; 10th tergum (Fig. 3C) entire,with very long setae. Aedeagus (Fig. 3B) withmedian lobe large, robust, obtuse at apicolateralcorners, acutely pointed apically; apical sclerotized area with the thin median longitudinal
suture. Endophallus with median longitudinalbands (Fig. 3D) each slender, long; expulsion
clasps (Fig. 3D) almost M-shaped, connectedeach other by a transverse plate, anterior plate
demarcated from posterior plate by oblique
suture, posterior plate weakly incurved, pointed
apically, laterally with a saucer-like depression;basal tube (Fig. 3D) with basal room large, subconical, tube body aciculare and thin. Parameres(Fig. 3B) straight, with its apical part long,
weakly swollen mesially; about 40 long, straightsetae occurring on the mesial margin of apicalpart, and additional 5 to 6 setae mesially on thepart just above the apical swollen part.
Female. Eighth venter entire; gonocoxites(Fig. 3G) each minutely serrate at posterior margin, with apicolateral tooth acutely pointed, andapicolaterally with a tuft of very long, straightsetae; 10th tergum rounded at posterior margin.
Spermatheca (Fig. 3F) robust, with capsulesmall, weakly turned mesially, RT-duct short,thin; spermathecal duct very thick, short with
two turns, with the duct between 1st and 2ndturns tightly coiled to form a tuberculous mass,basal valve very short, basal sclerotized duct narrow, straight.
Type series. Holotype (No. NSMT-I-C-200258

61in NMNS): ♂, Mt. Daisen (Yokote-michi, NW
slope 820 m), Daisen-cho, Tottori Pref., 7. ix.
1984, Y. Nishikawa leg. Paratypes: 2 ♀, Mt.
Kenashi, Tottori C., Tottori Pref., 23. v. 1989, N.
Tsurusaki leg.
Distribution. Japan (Honshu: Tottori Pref.).
Remarks. Stenus vernicosus sp. nov. belongs
to the species group of S. cirrus Benick. This
new species is closely allied to S. nyoirin Naomi,
2004, but it is clearly distinguishable from thelatter by the following characters: in male theaedeagal median lobe is broader in posterior half
(Fig. 3B), the endophallic expulsion clasps are
weakly divergent anteriorly, and connected eachother by a transverse plate, and its posterior plateis weakly incurved, pointed apically, and furnished laterally with a saucer-like depression(Fig. 3D); and in female the spermatheca is similarly structured, but the spermathecal duct behindthe 1st turn is distinctly shorter and thicker (Fig.
3F).
Etymology. The speciﬁc epithet of this newspecies is derived from the Latin adjective “vernicosus” which means “varnished” or “glossy”; infact the body of this new species is strongly varnished.
Achnowledgments
We thank Dr. V. Puthz (Burgmuseum, Schlitz,Germany) for his useful comment on the draft ofthis paper and also for his information on the taxonomy and distribution of Stenus bifoveolatus
Gyllenhal. The senior author (Naomi) thanks Mr.
A. B. Ryvkin (Russian Academy of Science) for
his kind suggestion regarding the taxonomic
position of S. aboblitus that we described in thispaper. We also thank the following entomologists
who collected the invaluable Stenus specimensthat we used for the present study: Mr. T. Kato(Hokkaido), late Mr. Y. Kurosawa (NMNS), Mr.
T. Niisato (Tokyo), Mr. N. Nishikawa, Mr. K.
Ohgi (Yamaguchi), late Dr. M. Sato (Nagoya),Dr. M. Tomokuni (NMNS) and Dr. N. Tsurusaki(Tottori Univ.).

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