Lathrobium nomurai Nakane, 1955

Sato, Yuya & Maruyama, Munetoshi, 2023, Taxonomy of the Lathrobium nomurai group (Coleoptera: Staphylinidae) from Northern Kyushu, Japan, with descriptions of two new species, Acta Entomologica Musei Nationalis Pragae (Acta. Ent. Mus. Natl. Pragae) 63 (1), pp. 111-124 : 112-117

Lathrobium nomurai Nakane, 1955

[Japanese name: Ô-kobane-naga-hanekakushi]

( Figs 1 , 2 , 9 )

Type material examined. HOLOTYPE: 3, Japan : Kyushu, “0000000424 / Sys. Ent / Hokkaido Univ. / Japan [ SEHU] // HOLOTYPE / Appended labeled by / ÔHARA / INARI / KANBE / SUZUKI / and / HIRONAGA / 2006 // NAKANE Coll. / SEHU / JAPAN / 1999 // Lathrobium / nomurai / Det. T. Nakane 1955 // Tsuruoka-Dô / Saeki / Oita Prf. / 3. X. 1954 / S. Nomura // 45–9 // HOLOTYPE ” ( SEHU) ( Fig. 1B ).

Additional material examined. 1 3, “[ JAPAN]: Oita-ken / Saeki-shi / Kariu / 90 m in alt. / [33.031, 131.895] / 27. X. 2019 / Tsubasa NOZAKI, leg.” ( KUM); 1 3, “[ JAPAN]: Oita-ken / Saeki-shi / Kariu / 90 m in alt. / [33.031, 131.895] / 9. XI. 2019 / Tsubasa NOZAKI, leg.” ( KUM); 1 3, 1 ♀, “ Oita –ken / Tsukumi-shi / Kamiaoe / 9. X. 2007 / T. Miyake leg.” ( TUA); 1♀, “(Tsuruoka Mine) / Saeki / Oita Pref. / Japan / 23-III-1955 / Coll. S-I. Uéno” ( TUA); 1♀, “( SAEKI) / Oita / Kyushu / XI–20.1946 / Coll. K. Kutosa” ( TUA); 1♀, “ JAPAN: Ôita Pref. / Saeki-shi / Kadomae / 12. Mar. 2020. / Tainaka” ( KUM).

Redescription. BL = 11.0– 15.4 mm, FBL = 5.5–5.8 mm (n = 8). Coloration: Body ( Fig. 1A ) reddish brown, moderately shining; maxillary palpi light red; legs reddish brown but basal part of tibia black or darken; mandible, scutellum, bases of antennomeres I–X black or darken; elytra reddish brown but elytral suture black; abdomen reddish brown, posterior margin of tergite VII and VIII light brownish red; tergite IX and X light red.

Head suborbicular, HL = 1.65–1.80 mm, HW = 1.65– 1.95 mm, HW/HL = 1.03, widest at the basal 1/5 of head; frontal area flattened; surface coarsely punctate; punctures sparser on frons and vertex, becoming denser toward posterior and lateral margins, with dark brown setae. Eyes very small, slightly protruding; longitudinal diameter of eye about 1/5 as long as temple in dorsal view. Antennae elongate, AL= 3.85–4.75 mm, AL/HL = 2.56, with whitish yellow setae; antennomere I robust, widest at apical 1/3; antennomere II slightly elongated, shorter than III; antennomeres III–X slightly narrow at base, widening towards apex, successively shorter and narrower toward apical antennomeres but IX and X almost same size; antennomere XI fusiform; relative length of antennomeres as follows: 1.83: 1.08: 1.23: 1.21: 1.20: 1.13: 1.13: 1.10: 1.07: 1.00: 1.20; relative maximum width of antennomeres as follows: 1.74:1.57: 1.43: 1.43: 1.31: 1.31: 1.31: 1.29: 1.00: 1.00: 1.03.

Pronotum oblong-oval, with anterior margin wider than posterior one, PL = 2.00– 2.20 mm, PW = 1.51–1.74 mm, PL/PW = 1.29, PL/HL = 1.24, PW/HW = 0.92, widest at apical 1/3; lateral sides of pronotum gently dilated to widest point, thence gradually convergent toward posterior margin; all corners obtusely rounded; disc sparsely covered with coarse and weak punctations except medial longitudinal line; punctures slightly sparser and less than on head, with brownish yellow setae.

Scutellum with sparse punctures. Elytra subtrapezoidal, widened posteriorly, EL = 1.08–1.30 mm, EW = 1.70–1.91 mm, EW/EL = 1.54, EL/PL = 0.56, EW/PW = 1.11; lateral margins almost straight; posterior corners rounded; disc covered with sparse and coarse punctations; punctations denser than on pronotum, with brownish yellow setae. Hind wing completely reduced. Legs with shortened tibiae and tarsi which are covered with golden setae; tarsomeres I–IV of protarsus dilated.

Abdomen elongate, gradually widened from segment III–V, thence contracted to the posterior end; each tergite covered with micropunctations and brownish yellow setae, distinctly long setae on each side near anterior margin; tergite X as long as posterolateral processes of tergite IX.

Male. Sternite VII ( Fig. 1C ) transverse, without posteromedian impression, posterior margin almost straight; sternite VIII ( Fig. 1D ) with posteromedian impression, with sparse setae; posterior margin of sternite VIII slightly asymmetric; sternite IX elongate.

Aedeagus ( Figs 2A–C ) 2.63 mm long, elongate; basal part of aedeagus with V-shaped impression; ventral process well sclerotized, slightly asymmetrical in ventral view, gradually narrowed toward apical 1/5, strongly narrowed toward apex, curved ventrally from 1/2 to apex; apical part of ventral process slightly curved toward left side in ventral view; apex of ventral process with small projection; basal and middle parts of ventral process slightly thicker than apex in lateral view; part above basal foramen transverse, with two projections at lateral side; dorsal plate sclerotized, widest at apical 1/4, gradually widened to the widest point at apical 1/4, thus contracted toward apex, with rounded apex; two tubes attached with apex of ventral process in between ventral process and dorsal plate; internal sac with sclerotized structures; ringed part connected with large flattened sac by sclerotized long-narrowed part.

Female. Sternite VIII ( Fig. 1E ) elongate, densely fringed with numerous setae, post-median margin straight. Differential diagnosis. This species is similar to Lathrobium fujimotoi from Mt. Kurodake, Oita Pref. in general appearance and aedeagal shape. However, this species can be easily distinguished from it by the combination of the following characteristics: 1) lateral side of ventral process of aedeagus straight; 2) internal sac without large sclerotized plate; 3) male sternite VIII slightly asymmetric and smaller than L. fujimotoi (in L. fujimotoi , each lateral side of ventral process is bulged at basal 1/3, the internal sac has a large sclerotized oval part and sternite VIII is symmetrical and larger).

Biology. Some specimens of this species collected from Kadomae by authors were found in the upper hypogean zone along mountain stream, at an altitude of about 70 m. We dug laterally 20–50 cm up the slope of this locality.

Distribution. Japan (Oita Pref., north of Kyushu).

Remarks. The aedeagus of the holotype is not available for examination. The additional specimens examined here have the characteristics of the antennae and male sternite VIII corresponding to the holotype, and we hence consider them as conspecific with the holotype. Their collection sites are near the type locality (Tsuruoka-Dô Cave, Saiki-City of Oita Prefecture, Japan) and the identical morphology of their aedeagus indicates that they all belong to the same species. Our illustrations of the aedeagus are based on these newly collected specimens.

Lathrobium fujimotoi Y. Watanabe, 2001 [Japanese name: Fujimoto-ô-kobane-naga-hanekakushi]

( Figs 3 , 9 )

Type material examined. HOLOTYPE: 3, Japan Kyushu , “Mt. KURODAKE / Shônai-cho / Oita / Kyushu / Japan / Sept. 21st. 1997 / Coll. H. Fujimoto // [HOLOTYPE] / Lathrobium (s. str.) fujimotoi / Y. Watanabe / 2001” ( TUA).

Additional material examined. 1 3, “ JAPAN: Oita-ken / Asono / Shonai-cho / Yufu-shi / Mt. Kurodake / 16. XI. 2021. / Y. Takagaki”.

Supplementary description. BL = 13.4–14.4 mm, FBL = 5.7–6.6 mm (n = 2). Coloration: Body reddish brown, moderately shining.

Head suborbicular, HL = 1.75–1.90 mm, HW = 1.75– 1.85, HW/HL = 0.99, widest at the basal 1/4 of head. Eyes very small, slightly protruding.

Pronotum oblong-oval, with anterior margin wider than posterior one, PL = 2.00– 2.23 mm, PW = 1.60–1.75 mm, PL / PW = 1.26, PL /HL = 1.16, PW /HW = 0.93, widest at apical 1/5.

Elytra subtrapezoidal, widened posteriorly, EL = 1.16–1.20 mm, EW = 1.78 mm, EW/EL = 1.51, EL/ PL = 0.56, EW/ PW = 1.06; lateral margins almost straight; posterior corners rounded. Hind wing completely reduced.

Male. Abdominal sternite VII transverse, with weak posteromedian impression; several setae at posteromedian area grown toward interior; sternite VIII with weak posteromedian impression.

Aedeagus ( Figs 3A–C ) 3.28 mm long, elongate; basal part of aedeagus with V-shaped impression; ventral process well sclerotized, slightly asymmetrical in ventral view, gradually narrowed toward apical 1/4, strongly narrowed toward apex, curved ventrally from 1/2 to apex; apical part of ventral process straight; apex of ventral process with small projection; basal and middle parts of ventral process slightly thicker than apex in lateral view; each lateral side of ventral process weakly bulged at basal 1/3 area; part above basal foramen almost pentagonal, with two projections at lateral side; dorsal plate sclerotized, widest at apical 1/4, gradually widened to the widest point at apical 1/4, thus strongly contracted toward apex, with subacute apex; two tubes attached with apex of ventral process in between ventral process and dorsal plate; internal sac large, with sclerotized and ringed part, including large sclerotized plate in dorsal side; sclerotized plate in internal sac with some spine lines dorsally; apical area of internal sac folded in complex way. Differential diagnosis. This species is similar to other species of the L. nomurai group in general appearance and aedeagus. However, this species can be easily distinguished from them by the combination of the following characteristics: 1) basal part of ventral process with V-shaped impression; 2) internal sac of aedeagus with large, sclerotized plate in dorsal side; 3) each lateral side of ventral process weakly bulged at basal 1/3 area; 4) apex of ventral process with small projection.

Biology. Holotype and additional specimen were collected from the upper hypogean zone and under stones in a deciduous broadleaf forest, at an altitude of about 850 m.

Distribution. Japan (Oita Pref., north of Kyushu).

Remarks. This species has been reported only from Mt. Kurodake, Oita Pref., Japan. See WATANABE (2001) for a detailed description of the species.

Lathrobium hikosanese Y. Watanabe, 1998 [Japanese name: Hikosan-ô-kobane-naga-hanekakushi]

( Figs 4 , 9 )

Material examined. 1 3, “Mt.Hiko / Soeda-Town / FukuokaPref./ [ JPN] / 2018. 10. 21. / H. Tanaka leg.” ( KUM); 1 3, 1 ♀, “[ JAPAN]: Fukuoka-ken. / Soeda-machi. / Hikosan. / 8. VI. 2019. / Tsubasa NOZAKI” ( KUM); 1 3, “ JAPAN / Fukuoka-ken / Umi-machi / Mt. Buccho / 25. X. 2015. / Naomichi Tsuji leg.” ( KUM); 1 3, “ JAPAN / Fukuoka-ken / Itoshima-shi / Mt. Iwara-yama (alt. 400 m) / 27. IV. 2014. / Naomichi Tsuji leg.” ( KUM); 1 3, “ JAPAN: Fukuoka-ken / Mizunashi / 15. VII. 2019. / Tanaka” ( KUM); 13, “Mt. Tachibana / Higashi-ku / Fukuoka / Fukuoka Pref. / JAPAN / 6. X. 2022. / Naomichi TSUJI leg.” ( KUM); 1 3, “Mt. Daisen / Kujyu Oita / 5. Vi. 1983 / S. Nomura” ( KUM); 1 3, “[ JAPAN] / Fukuoka-ken / Kitakyûshû-shi / Kokura-Minami-ku / Hiraodai / 33.769°N / 130.908°E / 22. V. 2021. / S. INOUE ” ( KUM); 1 3 “[ JAPAN]: Nagasaki-ken / Isahaya-shi / Kinsenji / [32.9739, 130.0879] / 1. X. 2022. / TANAKA H.” ( KUM).

Supplementary description. BL = 11.6–13.9 mm, FBL = 4.9–5.6 mm (n = 10). Coloration: Body reddish brown to reddish black, moderately shining.

Head suborbicular, HL = 1.43–1.68 mm, HW = 1.40– 1.65, HW/HL = 0.96, widest at the basal 1/3 of head. Eyes very small, slightly protruding.

Pronotum oblong-oval, with anterior margin wider than posterior one, PL = 1.75–1.95 mm, PW = 1.30–1.50 mm, PL / PW = 1.35, PL /HL = 1.20, PW /HW = 0.92, widest at apical 1/4.

Elytra subtrapezoidal, widened posteriorly, EL = 1.00– 1.25 mm, EW = 1.40–1.65 mm, EW/EL = 1.38, EL/ PL = 0.59, EW/ PW = 1.10; lateral margins almost straight; posterior corners rounded. Hind wing completely reduced.

Male. Sternite VII transverse, with weak posteromedian impression; sternite VIII with posteromedian impression; each side of posteromedian impression protruded weakly; lateral area of sternite VIII with slightly longer setae than median area.

Aedeagus ( Figs 4A–C ) 2.27 mm long, oblong; ventral process well sclerotized, asymmetric in ventral view, gradually narrowed toward 1/2, thus gradually narrowed toward apex, curved ventrally from 1/2 to apex; apical part of ventral process elongate, curved toward left side in ventral view; apex of ventral process with small projection; ventral process from basal to about 1/2 of area in ventral view two times thicker than that of apical part; basal and middle parts of ventral process ball-shaped, thicker than apical part in lateral view; part above basal foramen triangular, with two projections at lateral side; surrounding of basal foramen sclerotized; dorsal plate sclerotized, triangular with base at anterior margin, contracted toward apex, with acute apex; internal sac large, with sclerotized and ringed part; basal area of internal sac including two sclerotized long–narrow parts; each sclerotized part formed by gathering some thin plates; middle and apical area of internal sac flattened.

Differential diagnosis. This species is similar to L. daisensanum Y. Watanabe, 1998 , a member of the L. nomurai group described from Mt. Daisen-zan, Kagawa Pref., Shikoku, in general appearance and aedeagal shape. However, this species can be easily distinguished from it by the combination of the following characteristics: 1) dorsal plate of aedeagus triangular with base at anterior margin; 2) apical part of ventral process curved toward left side in ventral view; 3) middle area of ventral process of aedeagus gradually narrowed toward apex (while in L. daisensanum , apex of dorsal plate is truncate, apical part of ventral process of aedeagus is straight in ventral view, and middle area of ventral process of aedeagus is strongly narrowed toward apex).

Variation. Size and shape of aedeagus tend to vary by locality ( Fig. 4 ). It can be observed that individuals in the west tend to have larger aedeagus than those in the east.Although tendency cannot be observed, thickness and degree of curvature on apical part of ventral process also vary in each region; the smallest in Hiraodai, Fukuoka Pref. ( Figs 4E, K ), the largest in Mt. Iwara-yama, Fukuoka Pref. ( Figs 4H, N ).

Biology. Examined specimens were collected from the upper hypogean zone or under stones. Compared to other species of L. nomurai group, this species tends to be found in a shallow ground.

Distribution. Japan (north of Kyushu).

Remarks. This species has been described based on the specimens collected from only Mt. Hiko-san, Fukuoka Pref., Kyushu ( WATANABE 1998). This study revealed that this species occurs from Oita Pref. to Nagasaki Pref., and its distribution is wider than other species of the L. nomurai group in Kyushu ( Fig. 9 ). In addition, the aedeagus of this species shows a geographic variation in each region ( Fig. 4 ). We consider this variation as intraspecific because it is continuous, and the structures of internal sac are about the same in all examined specimens. See WATANABE (1998) for a detailed description.

Figures

Fig. 1. Lathrobium nomurai Nakane, 1955. A – habitus in dorsal view; B – labels of holotype; C – male sternite VII; D – male sternite VIII; E – female sternite VIII. Scale bars = 2.0 mm for A, 0.5 mm for C–E.

Fig. 2. Male aedeagus of Lathrobium nomurai Nakane, 1955: A – ventral view; B – lateral view; C – dorsal view. Scale bar = 0.5 mm. Abbreviations: AP – apical part of ventral process; BF – basal foramen; DP – dorsal plate; VP – ventral process. Black arrow indicates the V-shaped impression of basal margin of aedeagus.

Fig. 9. Map showing the distribution of the Lathrobium nomurai group in Kyushu, Japan. Black rhombus – L. nomurai Nakane, 1955; black triangle – L. fujimotoi Y. Watanabe, 2001; black circle – L. hikosanense Y. Watanabe, 1998; black square – L. yufuense sp. nov.; black pentagon – L. denchu sp. nov.; A–G – localities of L. hikosanense: A – Mt. Daisen; B – Mt. Hiko-san (type locality for L. hikosanense); C – Hiraodai; D – Mt. Buccho-zan; E – Mt. Tachibana-yama; F – Mt. Iwara-yama; G – Kinsenji Temple.

Fig. 3. Male aedeagus of Lathrobium fujimotoi Y.Watanabe, 2001:A – ventral view; B – lateral view; C – dorsal view. Scale bar = 0.5 mm.Abbreviation: SP – large sclerotized plate of internal sac.

Fig. 4. Male aedeagus of Lathrobium hikosanense Y. Watanabe, 1998 in each locality.A–C – Mt. Hiko-san (type locality): A – ventral view; B – lateral view; C – dorsal view. D, J – Mt. Daisen; E, K – Hiraodai; F, L – Mt. Buccho-zan; G, M – Mt. Tachibana-yama; H, N – Mt. Iwara-yama; I, O – Kinsenji Temple. Scale bars = 0.5 mm. Each locality referred to Fig. 9.