Malthinus orbiculatus N. Takahashi

Takahashi, Naoki, 2010, Notes on Malthinus mucoreus (Coleoptera: Cantharidae), with descriptions of two new related species from the Ryukyus, Southwest Japan, Zootaxa 2563, pp. 53-68 : 64-67

Malthinus orbiculatus N. Takahashi , sp. nov.

(Japanese name: Yaeyama-kurosuji-tsumaki-joukai) ( Figs. 7–8 , 37–45 )

Description. MALE. Similar to the preceding two species in general appearance. Body chiefly reddish yellow or orangish yellow, having palish yellow apical portions of elytra and some dark-coloured parts; ventral side of body and anterior part of head sometimes slightly paler, though distal parts of maxillary and labial palpi and mesal area of metaventrite sometimes darker; eyes black; vertexal marking on head, medio-longitudinal area of pronotum brownish black, and vertexal marking linguiform in outline but somewhat narrowed apicad; apical portions of mandibles, tibial spurs, and tarsal claws reddish brown; antennae, scutellum, 4th tarsal segments and rarely the adjacent parts dark brownish, though yellowish on basal parts of 1st antennal segments and often somewhat so on each distal portion and ventral side of basal few segments; elytron except for basal part and palish yellow apical area somewhat grayish, but dusky along sutural line and lateral margin and sometimes in the area just before apical yellowish spot; venter except for last two segments and lateral areas on each abdominal sternite sometimes dusky.

Head nearly as wide as long, 1.50 (1.44–1.52) times as wide as pronotum, weakly convex dorsad, faintly furrowed medio-longitudinally around the middle of posterior margin which is often hidden under the anterior margin of pronotum, somewhat flattened before vertex, weakly depressed apicad just before antennal pits, gently arcuate at apical margin of clypeus; surface puncticulate and lustrous before antennal sockets, rugulose in posterior area though somewhat smoother before vertex, finely granulate and matt on ventral side but almost impunctate and lustrous on stipes of maxillary palpi; eyes medium in size, semiglobular and prominent laterad, interocular distance 3.52 (3.13–3.53) times as large as radius of eye; antennae filiform, reaching about basal 9/13 of elytra, 1st segment subclavate, 2nd somewhat subclavate, 3rd to 11th subcylindrical, and relative lengths of antennal segments from base as follows—17.8: 11.6: 11.7: 13.4: 14.2: 13.7: 13.8: 13.3: 11.6: 10.4: 11.0.

Pronotum subquadrate, 1.05 (1.00–1.06) times as wide as long; disc mostly granulate though slightly rugulose on blackish marking, convex medio-dorsad, feebly and transversely swollen at middle, somewhat elevated in medio-posterial area but hollowed in the middle, evener than in M. mucoreus , subtruncate to faintly arcuate at anterior margin, obliquely narrowed apicad at front angles, obtusely rounded at hind angles, gently arcuate though faintly sinuate and weakly marginate at posterior margin; lateral margins subparallel but faintly and roundly protruded laterad at middle and shallowly emarginated mesad before hind angles. Scutellum subtrapezoidal and narrowed posteriad, covered with fine pubescence.

Elytra 2.63 (2.53–2.86) times as long as wide, each surface almost as in the preceding species. Legs moderately slender and simple; all claws simple; relative lengths of metatarsal segments from base as follows—16.7: 8.9: 6.3: 7.0: 7.9.

Meso- and metaventrites puncticulate and lustrous on their surfaces. Venter except for last abdominal sternite relatively smooth and lustrous but somewhat rugulose; 8th sternite widely and roundly emarginate at posterior margin; 9th relatively thin, arcuate along ventral surface of basal piece of genitalia in profile, mostly granulate and matt on surface in ventral view, broad at base, constricted apicad in basal fourth at sides, then gradually narrowed apicad in the rest part, angulately rounded at apex.

Male genitalia cymbiform in general appearance; ventral part of basal piece oblong though slightly narrowed apicad in apical part, with each subquadrately rounded apex somewhat swollen and slightly explanate mesad in dorsal view, widely and roundly emarginate at apical margin in caudal view; dorsal part of basal piece oblong, obtusely rounded at apical angles, somewhat narrowed basad and subtruncately rounded at base, concave medio-ventrad in apical half, bearing a projection in the middle at apical margin in dorsal view, warped dorsad and discoidally swollen in basal half in profile; lateral lobe subtriangularly dilated apicad with serrate outer side and pectinate apical margin in basal part in dorsal view, attenuate and densely covered with bristles on dorsum in apical part in profile.

Length of body: 3.7 (3.4–4.1) mm; width of body: 0.9 (0.8–1.0) mm; length of hind tibia: 1.2 (1.1–1.5) mm.

FEMALE. Similar to male, though body larger and somewhat darker in coloration, particularly so on elytra; metaventrite often dark brownish in most part; penultimate abdominal sternite sometimes dusky in mesal area.

Head 1.26–1.34 times as wide as pronotum; eyes slightly smaller than in male and interocular distance 4.08–4.41 times as large as radius of eye; antennae shorter than in male, reaching about basal 5/11 of elytra, and relative lengths of antennal segments from base as follows—19.9: 12.6: 11.6: 12.6: 13.4: 13.0: 12.7: 12.3: 10.9: 9.9: 10.7. Pronotum 0.98–1.09 times as wide as long. Elytra 2.19–2.76 times as long as wide. Relative lengths of metatarsal segments from base as follows—15.6: 8.5: 6.4: 7.5: 8.1. Eighth abdominal sternite subtrapezoidal in outline, narrowed apicad, subtruncate but distinctly and roundly emarginate in the middle at apical margin in ventral view. Female terminalia relatively stout; paraproct almost divided symmetrically into two parts, each part somewhat lanceolate-oblong in outline but not constricted basad in apical part and faintly curved mesad in dorso-lateral view; coxite somewhat linguiform in appearance but narrowed apicad, feebly depressed in mesal area on surface in ventral view, with a lapel at the base which is tapered at the mesal part compressed laterally.

Length of body: 4.0– 4.9 mm; width of body: 0.9–1.3 mm; length of hind tibia: 1.2–1.4 mm.

Type series. Holotype (Type No.3311, ELKU), male, Tindahanata, Yonaguni Is., Ryukyus, 23.iii.1995, N. Takahashi leg. Paratypes, RYUKYUS (Ishigaki Is.) Kabiraishizaki, 1 male, 21.iii.1996, T. Fukaishi leg. ( KURA). (Iriomote Is.) Mt. Uehara, 1 male and 1 female, 11.iii.1995, Y. Okushima leg. ( KURA). (Yonaguni Is.) Same locality as holotype, 1 female, 21.iii.1977, W. Suzuki leg. (TUA); 3 males and 6 females, 24.iii.1995, N. Takahashi leg. ( ELKU and NTC). Same data as holotype, 2 males and 6 females, ( ELKU and NTC). Near Mt. Urabe, 1 male, 20.iii.1977, W. Suzuki leg. (TUA); 1 female, 22.iii.1977, W. Suzuki leg. (TUA). Mt. Urabu, 8 males and 12 females, 18.ii.1990, Y. Okushima leg. ( KURA); 1 male and 1 female, 19.ii.1990, Y. Okushima leg. ( KURA). Mt. Donan, 4 males and 2 females, 9.iii.1995, Y. Okushima leg. ( KURA); 11 males and 4 females, 10.iii.1995, Y. Okushima leg. ( KURA). Mt. Kubura, 1 female, 23.iii.1995, N. Takahashi leg.; 1 male and 2 females, 19.iii.2005, R. Murao leg. ( ELKU and NTC). Higawa, 2 males, 21.iii.1995, M. Satô leg. (MSC).

Distribution. Japan: southern Ryukyus (Ishigaki Is., Iriomote Is. and Yonaguni Is.).

Infraspecific variation. Only one male specimen from Ishigaki Island has almost infuscate elytra with a small yellowish part just behind the pronotum on each elytron. The vertexal marking on the head is sometimes relatively smaller and weakly constricted at the posterior part. The male 9th abdominal sternite slightly varies in width in the apical portion, and is subtruncate at the apex in material from Iriomote Island, while it is somewhat angulately rounded from the other area.

Remarks. This new species is very similar to the preceding two species in general appearance, but is distinguished from the latter by the linguiform vertexal marking on the head, the dusky narrower stripes along the sutural line and lateral margins including ventral margins of the epipleura on the elytra, the structure of male genitalia, particularly with the roundly emarginated apex of the ventral part of basal piece and discoidally swollen base of the dorsal part of basal piece, the female 8th abdominal sternite with a relatively large emargination at the middle of the apical margin, and the somewhat linguiform coxites of the female terminalia.

Notes. “ Malthinus sp.”, which were collected on Yonaguni Island and referred to in Imasaka & Yamaji (1989), might belong to this new species.

Etymology. Derived from Latin orbis = disc; the specific epithet is associated with the discoidally swollen base of the dorsal part of basal piece in the male genitalia.

Figures

FIGURES 1 – 8. Habitus of Malthinus spp. 1 – 4, Malthinus mucoreus (Kiesenwetter) (1, male from Kagoshima Pref.; 2, female from Tsushima Is.; 3, type material; 4, type labels; 3 – 4, photos courtesy by Y. Okushima, taken at the Natural History Museum, London); 5 – 6, M. serrulatus N. Takahashi, sp. nov. (5, holotype; 6, female); 7 – 8, M. orbiculatus N. Takahashi, sp. nov. (7, holotype; 8, female).

FIGURES 37 – 41. Malthinus orbiculatus N. Takahashi, sp. nov., male. 37 – 38, apical portions of 9 th abdominal sternites, ventral view (37, from Yonaguni Is.; 38, from Iriomote Is.); 39, apical portion of ventral part of basal piece in genitalia, caudal view; 40 – 41, genitalia (40, dorsal view; 41, lateral view). Scales: 0.25 mm for FIGS. 37 – 39; 0.5 mm for FIGS. 40 – 41.

FIGURES 42 – 45. Malthinus orbiculatus N. Takahashi, sp. nov., female. 42, blackish markings on head and pronotum, an instance; 43, pronotum in outline, dorsal view; 44, apical margin of 8 th abdominal sternite in outline, ventral view; 45, terminalia, ventral view. Scales: 1.0 mm for FIG. 42; 0.5 mm for FIG. 43; 0.25 mm for FIGS. 44 – 45.