Malthinellus exiguus N. Takahashi, 2018

Takahashi, Naoki, 2018, A new soldier beetle Malthinellus exiguus sp. nov. (Coleoptera: Cantharidae) from the Ryukyus in southwestern Japan, with a key to Japanese species, Zootaxa 4403 (2), pp. 395-400 : 396-399

Malthinellus exiguus N. Takahashi , sp. nov.

( Figs 1 – 9 )

Type materials. Holotype (Type No. 3466, ELKU), male, Mt. Daruma—Mt. Ôtake , Kume Is., Ryukyus, Japan, 16.iv.1995, N. Takahashi leg.

34 Paratypes (13 males, 21 females): RYUKYUS (Okinawa Is.) Mt. Yonaha , 4.iv.1990, Y. Okushima leg. (1 male, KURA). Kunigami Vil., Ié-rindô near Benoki Dam , 21.iii.1998, N. Takahashi leg. (1 male, NTC). (Kume Is.) Same label as holotype (1 males and 2 females, ELKU; 2 males and 7 females, NTC). Same locality as holotype , 14.iv.1995, N. Takahashi leg. (2 females, NTC); 15.iv.1995, N. Takahashi leg. (3 males and 3 females, NTC). Mt. Ôtake , 15.iv.1995, N. Takahashi leg. (1 male, NTC). Mt. Daruma , 7.iv.1990, T. Ueno leg. (1 female, KURA); 8.iv.1990, T. Ueno leg. (2 males and 1 female, KURA); 9.iv.1990, T. Ueno leg. (1 male and 3 females, KURA). Nr. Mt. Daruma , 5.iv.1996, Y. Okushima leg. (2 females, KURA); 7.iv.1996, Y. Okushima leg. (1 male, KURA).

Diagnosis. Body yellowish orange to orange with brownish black elytra. Male genitalia: basal piece oboval in outline in ventral view, not produced at apex; outer lateral lobes slender in basal part, nearly securiform apically; inner lateral lobes developed, strongly curved medially in basal part, spathulate in apical part; penis composed of a pair of parts in dorsal view, each part somewhat Santoku knife-shaped with carinae along lateral margins in basal part. Female terminalia: paraprocts gently widened basally in outline in ventral view, approximately reaching the basal 2/3 of coxite in profile; coxite with lapel more or less reaching the basal 2/5 of the coxite at the median part in ventral view.

Description. MALE ( Fig. 1 ). Head, pronotum, scutellum, ventral side of body, and legs yellowish orange to orange, maxillary and labial palpi darkened, sometimes so on 2nd to 4th tarsal segments, somewhat more yellowish on abdominal sternites except for the two or three apical sternites; antennae dark brown but yellowish on basal halves of 1 st antennal segments; eyes black; elytra and hind wings dark brownish to black, however darker on the latter; apical halves of mandibles, tibial spurs and tarsal claws reddish brown and sometimes so on hind coxae along posterior margins, near hind angles of metaventrite.

Body elongate but somewhat stout, densely covered with pale brownish and recumbent pubescence, fitted with moderately longer pubescence around clypeus; antennae and lateral areas of elytra sparsely intermingled with pale bristles; antennae covered with darker bristles; legs covered with faintly darker bristles.

Head wider than long, 1.17 (in the holotype; range 1.09–1.21) times wider than pronotum; surface puncticulate, somewhat granulate and rugulose, slightly matt on dorsum though smoother and lustrous before and around vertex, finely granulate and matt on ventral side but almost impunctate and lustrous on stipes of maxillary palpi; eyes medium in size, interocular distance 3.41 (3.26–3.86) times larger than radius of eye; antennae filiform, slightly extending over elytral apices, relative lengths of antennal segments from base as follows—27.9: 16.1: 19.9: 22.2: 23.6: 24.6: 24.3: 23.9: 22.9: 21.9: 26.3.

Pronotum subquadrate, slightly broad, faintly dilated posteriorly, 1.31 (1.23–1.31) times wider than long; disc puncticulate, somewhat rugulose, lustrous on surface, gently convex medio-dorsally, faintly and transversely depressed at anterior third, feebly depressed in medio-posterial area, marginate on all margins and particularly so on anterior and posterior ones, sub-truncate on anterior margin, obtusely rounded on front angles, weakly arcuate posteriorly on posterior edge, obtuse on hind angles, flattened and gently arcuate laterally and feebly constricted on sides just before hind angles. Scutellum sub-trapezoidal and narrowed posteriorly, finely granulate and covered with fine pubescence.

Elytra 2.55 (2.38–2.55) times longer than wide, reaching last abdominal tergite; each elytron puncticulate, lustrous around humerus, weakly marginate along sutural line and lateral margin except for areas around humerus and apex, longitudinally punctate in rows with several rather undefined costae, faintly rugulose: particularly so in mesal half but smoother around humerus and apex, the punctures becoming indistinct distally in other area though relatively distinct along lateral margin.

Mesoventrite, mesepimera, metaventrite, and metanepisterna puncticulate and lustrous on their surfaces but sometimes faintly matt on mesoventrite and mesepimera. Abdominal sternites, except for 9th sternite puncticulate, feebly rugulose and lustrous; 8th sternite widely and obtusely emarginate on posterior margin; 9th sternite nearly oblong in outline and gently convex medio–ventrally in ventral view, gradually narrowed in anterior half which is hidden under the penultimate sternite, more narrowed behind faint angulations on sides in posterior portion, weakly produced posteriorly and bilobate around apex, puncticulate and finely granulate and matt in posterior half on ventral surface, arcuate postero-ventrally in posterior half in profile.

Male genitalia ( Figs. 3–8 ) stout, nearly oboval but apically and basally flattened in outline in dorsal view: basal piece gently convex medio-ventrally, oboval but apically flattened in outline in ventral view, weakly curved dorsally in apical part in profile, medio-longitudinally furrowed on ventral surface with a carina on dorsal surface which reaches just behind the apex; outer lateral lobe elongate and curved medio-dorsally, slender in basal part, and nearly securiform in apical part; inner lateral lobe prolonged medio-dorsally, strongly curved medially in basal part, spathulate but feebly warped dorsally in apical part, and roundly sub-triangulate around apex in profile; penis composed of a pair of parts in dorsal view, each part somewhat Santoku knife-shaped with carinae along lateral margins in basal part.

Body length: 3.2 (2.4–3.9) mm; width: 0.8 (0.7–1.0) mm.

FEMALE ( Fig. 2 ). Similar to male, but body slightly larger in general appearance; last abdominal sternite sometimes faintly more orange colored than the other ones. Head 1.04–1.16 times wider than pronotum; eyes slightly smaller than in male and interocular distance 3.68–4.14 times larger than radius of eye; antennae shorter than in male, approximately reaching the basal 2/3 of elytra, and relative lengths of antennal segments, from base to apex, as follows—29.0: 16.2: 19.9: 20.8: 21.4: 22.2: 22.1: 21.7: 20.1: 18.8: 23.1. Pronotum 1.24–1.31 times wider than long. Elytra 2.34–2.48 times longer than wide. Eighth abdominal sternite gradually narrowed posteriorly, somewhat more narrowed in about posterior 1/4, obtusely and roundly emarginate in the middle on posterior margin in ventral view, moderately convex medio-ventrally, its surface puncticulate, relatively smooth and bright.

Female terminalia ( Fig. 9 ) somewhat stout; paraproct almost divided symmetrically into two parts, each part nearly oval in outline, narrowed dorso-medially in apical part, slightly rounded at apex in dorso-lateral view, approximately reaching the basal 2/3 of coxite in profile; coxite sub-conical but generally flattened in appearance, weakly and obtusely protruded laterally in the middle on outer margin, swollen along outer margin, feebly depressed in medio-longitudinal area along inner margin in ventral view, with a lapel at the base more or less reaching the basal 2/5 of the coxite at the median part.

Body length: 2.8–4.1 mm; width: 0.8–1.2 mm.

Distribution. Japan: central Ryukyus (Okinawa Is. and Kume Is.).

Remarks. This new species is very similar to Malthinellus masatakai Takahashi & N. Takahashi, 2007 from the Okinawa Island in general appearance, but is distinguishable from the latter by the genital structure: in males by the elongate, apically nearly securiform outer lateral lobe, and the long inner lateral lobe and, in females, by the relatively stout coxites and the gently and basally widened paraprocts in outline in ventral view with less warped apical parts in dorso-lateral view.

The terminalia of a single female specimen from the Tonaki Island, located between the Okinawa and Kume Islands, shows intermediate morphological features between M. exiguus and M. masatakai . For this reason, it is felt that further investigations are needed to better understand the taxonomic meaning of morphological differences.

I propose that the Japanese name of this new species is “Kumejima-futairochibi-jôkai”.

Etymology. Derived from Latin exiguus = small; with reference to the small body size.

Determination key to the Japanese Malthinellus (modified from Takahashi & Takahashi, 2007)

1. Pronotum and elytra brownish black or dark brown........................................................... 2

- Pronotum yellowish orange to orange, elytra dark brown...................................................... 3

2. Pronotum and elytra brownish black............................................... M. bicolor Kiesenwetter, 1874

- Pronotum and elytra dark brown................................................... M. tsuchidai Takahashi, 2016

3. Head blackish brown............................................................... M. chujoi (Wittmer, 1961)

- Head yellowish orange to orange......................................................................... 4

4. Male genitalia with poorly developed inner lateral lobes, outer lateral lobes extended vertically; female terminalia with rela- tively elongate coxites in ventral view, paraprocts basally widened in outline in ventral view and faintly warped around apex in dorso-lateral view................................................ M. masatakai Takahashi & N. Takahashi, 2007

- Male genitalia with well-developed inner lateral lobes, outer lateral lobes slender in basal part and nearly securiform in apical part; female terminalia with relatively stout coxites in ventral view, paraprocts gently widened basally in outline in ventral view and less warped around apex in dorso-lateral view............................. M. exiguus N. Takahashi , sp. nov.

Figures

FIGURE 9. Female terminalia of Malthinellus exiguus N. Takahashi, sp. nov., ventral view (setae omitted on the right side). The arrow representation is the same as that in FIGS 3–8. Abbreviations: c, coxite; lp, lapel of coxite; pp, paraproct. Scale: 0.125 mm.

FIGURES 1–2. Habitus of Malthinellus exiguus N. Takahashi, sp. nov., dorsal view. 1, male; 2,female.Scales: 1.0 mm.

FIGURES 3–8. Scanning electron microscopy images of the male genitalia of Malthinellus exiguus N. Takahashi, sp. nov. 3, dorsal view; 4, dorso-basal view; 5, dorso-lateral view; 6, dorsal view showing the positions of parts presented in the FIGS 7– 8; 7, inner and outer lateral lobes, enlarged dorsal view; 8, outer lateral lobe, enlarged dorso-basal view.The arrow in the right margin explains the meaning of the terms “basal” and “apical”, as used in description: they correspond to the “anterior” and “posterior”, respectively. Abbreviations: bp, basal piece; il, inner lateral lobe; ol, outer lateral lobe; p, penis. Scales: 0.2 mm (FIGS 3–5); 0.1 mm (FIGS 7–8).