Pachysternum sulawesicum Fiká

Fikáček, Martin, Jia, Fenglong & Prokin, Alexander, 2012, A review of the Asian species of the genus Pachysternum (Coleoptera: Hydrophilidae: Sphaeridiinae), Zootaxa 3219, pp. 1-53 : 46-48

Pachysternum sulawesicum Fiká č ek, 2006

( Figs. 11 , 17 , 35, 70)

Pachysternum sulawesicum Fikáček, 2006: 152 .

Pachysternum sulawesicum: Short & Fikáček (2011: 113, catalogue) .

Type locality. Indonesia, Sulawesi, Malino env., E of Ujung Pandang [coordinates ca. 5°16'31''S, 119°50'59''E].

Type material examined: Holotype: male ( NHMW): “ S-SULAWESI 1992 / Umg. Malino (27) / E Ujung Pandang / leg. Jäch 29.IV.”. Paratypes: 2 spec. ( NMPC): “S-SULAWESI 92 / Umg. Malino (27) / leg. Schödl 29.4.”; 1 male ( NHMW): “N-SULAWESI 1992 / Umg. Modoindingo / NÖ Kotamobagu (12) / leg. Schödl 19.IV.”.

Additional material examined. INDONESIA: Sulawesi: 1 spec. ( ASKC): 5 km SE Batu Putih , 250 m a.s.l., 1°32'43''N 125°7'29''E, 18.ii.2009, lgt. A. Skale.

Differential diagnosis. Pachysternum sulawesicum may be easily distinguished from other species by the coloration of elytra (which typically bears large apical horse shoe-shaped pale spot and small humeral pale spot), continually arcuate outer margin of anterior tibia and entirely dark pronotal disc. Pale specimens of P. sulawesicum may resemble dark specimens of P. nigrovittatum by the elytral pattern, but may be easily distinguished by the shape of anterior tibiae and coloration of pronotum mentioned above (anterior tibiae are distinctly bisinuate on outer margin and pronotum is pale with large M-shape spot in P. nigrovittatum ). Dark specimens of P. sulawesicum are rather similar to dark specimens of P. kubani , but may be distinguished from the latter by uniformly arcuate anterior tibia (deeply sinuate in P. kubani ). Distinct (but vaguely limited) humeral spot along with pale apical portion of elytra is rarely present also in the specimens of P. apicatum , which may be distinguished by at least slightly angulate outer margin of anterior tibia and by the shape of the median lobe (wide in basal third and then narrowing apicad in P. apicatum , nearly parallel-sided throughout in P. sulawesicum ).

Redescription. Body widely oval, shape of elytra slightly sexually dimorphic, female with distinctly pronounced humeral portion of elytra. Body length 2.5–3.6 mm (holotype: 2.6 mm); body width 1.5–2.2 mm (holotype 1.9 mm).

Coloration. Clypeus and median portion of frons pale reddish, lateral portions of frons dark brown. Pronotum dark brown with widely reddish anterolateral corners and median portion of anterior margin. Elytron dark brown with sharply delimited pale reddish spot at the base of elytral interval 5, small pale reddish spot in anterolateral corner, and large horseshoe-shaped pale reddish spot at apex; the apical spot reaching more anteriad on intervals 2, 5– 7 and 10. Ventral surface of head brown, thoracic sclerites dark brown, legs and abdominal ventrite 5 pale reddish.

External morphology. Clypeus with moderately coarse and rather sparse punctation consisting of nearly uniform-sized punctures divided by ca. 2–3× of puncture diameter. Frons with slightly coarser punctation than on clypeus, consisting of punctures of two slightly different sizes separated by ca. by 1.5–3× of puncture diameter. Interstices without microsculpture. Larger punctures on pronotum rounded, much larger than small punctures, small punctures scar-like, divided by ca. 2–3× of puncture width. Pronotal interstices without microsculpture. Prosternum with weak or nearly indistinct median carina. Elytral series consisting of large, shallow punctures; interval punctation with moderately large semicircular punctures much smaller than serial ones, interval punctation consisting of two slightly different sizes of punctures, larger punctures setiferous; interstices with moderately developed mesh-like microsculpture. Elytral series indistinctly impressed. Preepisternal elevation of mesothorax without posterolateral pits. Femoral lines on metaventrite slightly angulate; median portion of metaventrite bearing moderately large and dense setiferous punctation, interstices without microsculpture; lateral portions with very coarse and dense, densely pubescent punctation. Outer margin of anterior tibia very slightly bisinuate, outer series of spines not interrupted.

Male genitalia ( Fig. 35). Tegmen and median lobe 1.3 mm long. Phallobase ca. twice as long as parameres, slightly asymmetrical basally, without distinctly detached manubrium. Median lobe widest at midlength, weakly narrowing apicad, apex narrowly rounded; gonopore subapical, rather indistinct; lateral pubescent lobes narrow, developed only subapically. Median projection of sternite 9 with deep V-shaped emargination apically.

Variation. Rather variable species, the variability concerns the coloration, dorsal microsculpture and the height of median carina of the prosternal plate. The additional specimen examined (Batu Putih env.) has the pale spots of elytra much more extended than the type specimens redescribed above, with the elytron colored as follows ( Fig. 70 c): interval 1 black, whole interval 2 pale reddish, basal pale spots present on intervals 2–4 and 7–10; basal spot similar to type specimens, but reaching more anteriad on intervals 3–6; lateral margin of elytron widely pale reddish throughout. The coloration of the pronotum and the head of this specimen corresponds with the type specimens redescribed above. Dorsal microsculpture of elytral intervals varies from moderately distinct (in the holotype and the additional specimen from Batu Putih env.) to rather indistinct (in some paratypes). Median carina of prosternal plate is rather obsolete in some specimens and therefore seemingly absent, but it may be still detected on SEM micrographs of these specimens.

Biology. Unknown.

Distribution. Known from two localities in northernmost Sulawesi and one locality in southern Sulawesi. Most probably widely distributed throughout the island.

Figures

FIGURE 70. Pachysternum sulawesicum, general habitus (a, c: dorsal view, b: dorsolateral view). Localities of the specimens: a – b: Sulawesi, Malino env. (holotype, male); c: Sulawesi, SE of Batu Putih.

FIGURES 1 – 11. General morphology of Asian Pachysternum. 1: mentum of P. nigrovittatum; 2: maxillary palpus of P. n i g ro - vittatum; 3: maxillary sucking disc of male of P. nigrovittatum; 4: head of P. curvatum, ventral view; 5: antenna of P. c u r v a t u m; 6 – 8: prothorax of P. nigrovittatum (6: posterior view, 7: lateral view, 8: ventral view); 9 – 11: prosternal plate (9: P. h a e m o rrhoum, 10: P. rugosum, 11: P, sulawesicum).

FIGURES 12 – 25. General morphology of the Asian Pachysternum. 12 – 14: pronotal punctation (12: P. nigrovittatum, 13: P. haemorrhoum, 14: P. r u g o s u m); 15: meso- and metathorax of P. nigrovittatum, ventral view; 16 – 19: preepisternal elevation of mesothorax (16: P. haemorrhoum, 17: P. s u l a w e s i c u m, 18: P. apicatum, 19: P. rugosum); 20 – 21: surface sculpture of metaventrite mesally and laterally of femoral line (20: P. nigrovittatum, 21: P. haemorrhoum); 22: elytral punctation of P. nigrovittatum; 23: scutellum of P. nigrovittatum; 24: anterior leg of P. nigrovittatum; 25: abdomen of P. nigrovitattum.