Bull. Natl. Mus. Nat. Sci., Ser. A, 33(4), pp. 181–191, December 21, 2007

A Taxonomic Revision of the Clavigerine Genus Microdiartiger(Insecta, Coleoptera, Staphylinidae, Pselaphinae)Shûhei Nomura
Department of Zoology, National Museum of Nature and Science,
3–23–1 Hyakunin-cho, Shinjuku-ku, Tokyo 169–0073 Japan
E-mail: nomura@kahaku.go.jp

Abstract The clavigerine genus Microdiartiger K. Sawada known from Japan is redefined as anindependent genus from the allied genus Diartiger Sharp. A new species, M. thinhi from Vietnam
is described.
Key words : Pselaphinae, Clavigeritae, Microdiartiger, Vietnam, Japan.

The clavigerine genus Microdiartiger was defined by K. Sawada (1964) together with a description of the type species M. japonicus collected from Mt. Makinoo-san, Osaka Prefecture,
Honshu, Japan. This genus was separated fromthe allied genus Diartiger Sharp by having 1) thehead and pronotum covered with short andsuberect hairs, 2) the elytra with linear microsculpture, and 3) the elongate and simple midtrochanter (spinulate in Diartiger).
Besuchet (1986) considered Microdiartiger tobe identical with Diartiger, and surppresed thegeneric name Microdiartiger as a junior synonym of Diartiger. Nomura (1997) followed hissystem and redescribed the type species as Diartiger japonicus (K. Sawada).
In the course of my recent studies, a newspecies of this lineage was discovered from Vietnam. The author concluded that Microdiartiger
should be revived as an independent genus. In
the present study, the genus Microdiartiger is redefined with descriptions of a new species and aredescription of the type species M. japonicus K.
Sawada on the basis of SEM observations. Systematic relationship of these genera is discussed.
Materials and Methods
The specimens examined for the present study
were collected by Tullgren funnel and flight in-tercept trap (FIT). The type specimen of the newspecies was collected by FIT which is of thesame type as used in Nomura and Idris (2004).
Most of the material examined were preserved indry condition. For detailed examination and dissection, they were washed and dissected in 70%
ethanol. Dissections were made using standard
techniques, genitalia and small parts were mounted in Canada balsam on a small grass slide onthe same pin with the specimen by the method ofMaruyama (2004). Leica MZ Apo microscope
was used for observation in this study.
For the SEM observation, a specimen of M.
japonicus was dried, coated with gold, and observed under the accelerating voltage (AV)
10–20 kv by JEOL JSM-6380LV. The other noncoated specimens were examined under lower AV
0.9 kv.
Genus Microdiartiger K. Sawada, 1964
[Japanese name: Hime-higebuto Arizukamushi Zoku]
Microdiartiger K. Sawada, 1964: 12. Type species: Microdiartiger japonicus K. Sawada, by original designation.

Body small to middle-sized, elongate, broadened in pronotum and abdomen.
Head longer than wide, subcylindrical; clypeus
very short; frons convex, strongly narrowed anteriad; vertex weakly convex; genae strongly projected laterad before eyes; postgenae broad, an-182Shûhei Nomura

Fig. 1. Microdiartiger spp. A, M. thinhi sp. nov., male habitus in dorsal view; B, ditto, in ventral view; C, M.
japonicus K. Sawada, male habitus in dorsal view; D, ditto, in ventral view.

Fig. 2. Microdiartiger thinhi sp. nov., male. A, Head and prothorax in dorsal view; B, ditto, in ventral view; C,head in lateral view; D, ditto, in anterior view; E, left antenna in dorsal view; F, right antenna in ventral view;
G, mouthparts in ventral view; H, elytra in dorsal view.

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Shûhei Nomura

gulate in posterior parts. Eyes developed andovoid. Antennae short and elongate, thickened
distally, truncate at apex; segments I and II very
short; III longer than wide, weakly broadened
distad; IV largest, longer than wide, with a large
circular concavity containing short conical setae
at apex. Mouthparts put into buccal cavity, reduced, but less than in Diartiger; maxillary palpi
short and elongate, fusiform in apical part.
Pronotum about as long as head, about as longas wide, subglobose, densely covered withcoarse, irregular reticulation on whole surface,sparsely with short suberect setae on dorsal orlateral sides. Elytra slightly wider than long,
weakly narrowed anteriad, covered with linear
microsculpture on basal, lateral and apical surfaces; each elytron with indistinct basal fovea(e)and longitudinal carinae in mesal part, with ashort trichome at apical part. Legs short, thick;mid femora each with a spine on posterior side inmale; mid tibiae elongate, each with a denticle
near apex in male.
Abdomen very large, about as wide as elytra,
weakly convex on dorsal side, rounded on lateraland posterior margins; composite tergum formedby tergites IV to VI very large, strongly concavein basimedian part, with trichomes in basal part;
paratergites IV to VI well demarcated, each elongate; tergites VII to VIII each short, narrowed
posteriorly; sternites III to VIII well demarcated,each transverse, successively narrowed toward
apex.
Male genitalia almost symmetrical; median
lobe elongate, narrowed toward apex, divided
into basal bulb and apical lobe, with a large elliptical membranous part on basidorsal side.
Remarks. The genus Microdiartiger is similar to the genus Diartiger in having the four-segmented antenna with two large apical segments.
However, it is separable by the mid trochanter
without spine on the posterior side and the elytra
covered with linear microstculpture.

Microdiartiger has been synonymized with Diartiger by Besuchet (1986). However, Microdiartiger should be isolated as an independent genus,
because not only it is a monophylectic unit, butalso the remaining Diartiger is monophyletic.
The monophyly of the genus Microdiartiger is
supported by two autoapomorphic characters: 1)
the head and pronotum sparsely covered withthick suberect setae, and 2) the elytra denselywith longitudinal linear microsculpture. The twoknown species of this genus share some commoncharacters, for example, the mouthparts less reduced than in Diartiger, though, they are primitive characters.
On the other hand, the monophyly of the remaining Diartiger is distinct. It is supported by
the following apomorphic characters: 1) the midtrochanters each with a large, strong spine on theposterior side, 2) the strongly reduced mouthparts with the short, hammer-like maxillary palpus (large and fusiform in Microdiartiger), 3) themetasternum densely setose along the medianline.
Microdiartiger thinhi sp. nov.
(Figs. 1A, B, 2–4)

Etymology. This species is dedicated to aVietnamese dipterologist, Dr. Ta Huy Thinh for
his kind assistance in the author’s fieldworks inVietnam.
Holotype male, Mt. Tam Dao (950 m), by FIT,Vinh Phu Prov., N-Vietnam, 13–21. v. 2003, S.
Nomura leg. (NSMT).
Male. Body (Fig. 1A) length 1.98 mm, width
0.71 mm, elongate, narrowed in head and pronotum, color reddish brown and shiny.
Head (Fig. 2A–D) widest at anterior margin ofgenae and just behind eyes, weakly convex, irregularly reticulate on dorsal surface; clypeus gentlyprojected anteriad; frons convex, weakly narrowed just before eyes, strongly narrowed anteri-Fig. 3. Microdiartiger thinhi sp. nov., male. A, Elytra enlarged; B, meso- and metathoraces in ventral view; C,left fore leg in ventral view; D, left mid leg in ventral view; E, right hind leg in ventral view; F, abdomen indorsal view; G, ditto, basilateral part enlarged; H, ditto, in ventral view.

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186Shûhei Nomura

ad to form a short longitudinal carina in anterior
part; vertex weakly convex, with a pair of strong,round dorsal tentorial pits just above eyes; genae
strongly concave behind antennal bases. Eyes
each composed of about 25 facets. Antennae(Fig. 2E, F) 0.40 mm in length; segment I very
short, annular, invisible in dorsal view; II slightly
longer than I, as wide as I, broadened apically;
III about twice as long as wide, weakly thickened
apicad, with short, thick setae in apical part; IVlargest, longer than IIIIII, 2.4 times as longas wide, subcylindrical, sparsely covered withshort setae in lateral surface; relative length(width) of each segment to width of segment I:
0.8(1.0) : 0.8(1.0) : 2.2(1.2) : 4.0(1.7). Mouthparts
small; labrum very small, wider than long, shallowly emarginate on anterial margin; mandibles
very small, triangular in anterior view; maxillary
palpi short, fusiform in apical part, with a group

Fig. 4.

of short setae at apex.
Pronotum slightly larger than head, slightly
longer than wide, widest at anterior 2/5, then narrowed anteriorly, with a pair of basilateral foveae
at posterior 1/4, with a shallow median longitudinal groove in basal 2/3 on dorsal side. Meso- andmetasterna very large, gently convex, almost
smooth on middle part, with a group of small
setae in posteromedian part, densely covered
with linear microsculpture on lateral sides. Elytra
weakly convex, sparsely with thick setae; each
elytron with a basal fovea at middle of anterior
margin, with adsutural and median carinae in its
full length, with lateral carina extending frombasal fovea to posterior 1/3, with short trichomeat middle of posterior margin. Legs short, stout;
mid femora thick in base, weakly narrowed apicad, each with a large, triangular spine on posterior side at base; mid tibiae narrow at base, weakly

Microdiartiger thinhi sp. nov., male genitalia. A, Ventral view; B, lateral view; C, dorsal view.

Fig. 5. Microdiartiger japonicus K. Sawada, male. A, Head and prothorax in dorsal view; B, ditto, in ventralview; C, head in lateral view; D, ditto, in anterior view; E, left antenna in dorsal view; F, right antenna in ventral view; G, ditto, apical part enlarged; H, mouthparts in anterior view.

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broadened apicad, each with a very short denticle
at apical 1/4 on inner side.
Abdomen longer than elytra, slightly wider
than long, sparsely covered with short, thicksetae in posterior part; composite tergum strongly concave in basimedian part, with a pair ofshort oblique trichomes just behind elytral trichomes, with a pair of basilateral foveae just outside of trichomes; paratergites IV to VI well demarcated; IV elongate, widest, with a large semicircular trichome in basal part; V about as longas IV, slightly narrower than IV, elongate, quadrangular; VI slightly shorter than V, elongate, triangular; tergite VII short, transverse, sparselywith thick erect setae; VIII small, nearly triangular in posterior view; sternites III to VIII feebly
convex; III short; IV largest, about three times aswide as long; V 0.6 times as long as IV, covered
with linear microsculpture on lateral sides; VIshort, with linear microsculptureson lateral sides;
VII very short in middle part, about as long as VI
in lateral parts, densely covered with minutereticulation; VIII short, transverse, nearly Ushaped, with a pair of short, thick setae at posteromedian part, densely covered with minute
reticulation on lateral sides.
Male genitalia (Fig. 4) weakly sclerotized;
basal bulb ovoid, strongly narrowed distad, withwell projected basal foramen on ventral side; apical part strongly narrowed, ventrally curved toward apex; endophallus with a very long andslender sclerite; the sclerite slightly curved, feebly broadened and bifurcate at apex in lateralview.
Female. Unknown.
Distribution. Vietnam (Mt. Tam Dao).
Remarks. This new species resembles thetype species, M. japonicus K. Sawada in having
the short and thick antennae, the pronotum withshort and thick suberect setae, the elytra covered
with linear microsculpture, and the similar structure of the male genitalia. However, it is easily

separated by the large body and the composite
abdominal tergum with broad basimedian concavity and the oblique trichomes (narrow basimedian concavity and transverse trichome in that ofM. japonicus).
Microdiartiger japonicus K. Sawada, 1964
[Japanese name: Hime-higebuto-arizukamushi](Figs. 1C, D, 5–7)
Microdiartiger japonicus K. Sawada, 1964: 13 (Type locality: Mt. Makinoo-san, Osaka Pref.); Besuchet, 1986:263; Nomura, 1989: 293; 1997: 91; 1999: 190.

Specimens examined. 1 female, Hiekawa,Shizuoka Pref., 25. vii. 1996, YR. Sawada leg.
(NSMT). See Nomura (1997, 1999) for the dataof other specimens.
Male. See Nomura (1997) for the generalcharacters except for the microstructure observed
by SEM shown below: head and pronotum rugosely sculptured, sparsely covered with thicksuberect setae on dorsal and lateral surfaces; antennal segments II to III reticulate; IV smooth onlateral sides; mouthparts less reduced than in Diartiger; labrum short, transverse, narrowly emarginate at middle on anterior margin, with a transverse sulcus at middle; mandibles shortened,each with a short denticle and a fovea at externalpart; maxillary palpi elongate, each nearly
fusiform in apical part, with two thick setae on
ventral side; labium transverse, with very shortand unisetose labial paipi and quadrate mentum
with two pairs of setae at basimedian part; elytra
densely covered with linear microsculptures,sparsely with large recumbent setae, with a deep
longitudinal sulcus and a longitudinal carina
along outer margin on inner side (Fig. 6F), withan indistinctly demarcated stridulatory file justinside posterolateral corner on inner side (Fig.
6G); hind wing developed (Fig. 6H); metasternum densely covered with longitudinal linear microsculptures; composite tergum of abdomen

Fig. 6. Microdiartiger japonicus K. Sawada, male. A, Mouthparts in ventral view; B, elytra, basal part enlarged;
C, ditto, basal part; D, ditto, apical part; E, ditto, in ventral view; F, lateral carina of elytra, enlarged; G,stridulatory file (?) on elytra, enlarged, H, right hind wing in dorsal view.

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A Taxonomic Revision of Microdiartiger

large, almost smooth in median part, reticulate inposterior part; sternites III to V densely covered
with linear longitudinal microsculpture on lateralsides; VI to VIII each densely with reticulation
as a whole.
Distribution. Japan(Honshu,Shikoku,Kyushu).
Remarks. This species is characterized by thesmall body (1.38–1.49 mm in the male, 1.50–1.58 in the female in length), the composite abdominal tergum with a narrow basimedian concavity and a pair of large transverse basilateraltrichomes, and the male sexiual characters of themid legs.
Acknowledgements
I wish to express my hearty thanks to Dr.
Shun-Ichi Uéno for his critical reading of themanuscript. My cordial thanks are due to Dr. Vu
Quang Con and Dr. Ta Huy Thinh for their kindassistance for my field work in Vietnam.
This study is supported in part by the Grantin-aid No. 09041167 for Field Research of the191

Monbusho International Scientific Research
Program, Japan and by the Grant-in-aid No.
18208006 of the Japan Society for the Promotionof Science (JSPS).
References
Besuchet, C., 1986. Synonymes et homonyme nouveauxde quelques genres de Psélaphides (Coleoptera). Revuesuisse de Zoologie., 93: 257–264.
Maruyama, M., 2004. A permanent slide pinned under aspecimen. Elytra, Tokyo, 32: 276.
Nomura, S., 1989. In: Hirashima, Y. (ed.) A Check List ofJapanese Insects, 1. 1767 pp. Isseido, Fukuoka.
Nomura, S., 1997. A systematic revision of the clavigerine genus Diartiger Sharp from East Asia (Coleoptera,Staphylinidae, Pselaphinae). Esakia, Fukuoka, (37):
77–110.
Nomura, S., 1999. Records of some species of Diartiger(Coleoptera, Staphylinidae, Pselaphinae) from Shikoku,Japan. Elytra, Tokyo, 27: 189–190.
Nomura, S. and A. G. Idris, 2004. A new species of thegenus Awas (Coleoptera, Staphylinidae, Pselaphinae)
from the Malay Peninsula. Elytra, Tokyo, 32: 329–335.
Sawada, K., 1964. Two new genera of pselaphid-beetles
from Japan. Entomological Review of Japan, 17: 11–14.

Fig. 7. Microdiartiger japonicus K. Sawada, male. A, Meso- and metathoraces in ventral view; B, right fore leg
in ventral view; C, right mid leg in ventral view; D, right hind leg in ventral view; E, right hind tarsus in ventral view; F, abdomen in dorsal view; G, ditto, basilateral part enlarged; H, ditto, in ventral view.