Pachysternum curvatum Orchymont 1925
Creators: name: Fikáček, Martin
name: Jia, Fenglong
name: Prokin, Alexander
Publisher: name: Zenodo
Year: 2012
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Coleoptera
Hydrophilidae
Pachysternum
Pachysternum curvatum

description: Pachysternum curvatum Orchymont, 1925
(Figs. 4–5, 37, 40, 56, 72)
Pachysternum curvatum Orchymont, 1925: 201.
Pachysternum curvatum: Orchymont (1926a: 224, identification key); Orchymont (1926b: 374, second, more detailed English description with the specification of type specimens); Hansen (1999: 307, catalogue).
Type locality. Philippines, Luzon island, Imugan.
Type material examined. Lectotype (here designated): 1 male (IRSNB): “ Imugan, Luzon // Cotype // Pachysternum / curvatum // coll. d’Orchymont // Para- / type” [considered as a paratype by Orchymont (1926b)]. Paralectotypes: 1female (IRSNB): same locality data as the lectotype [considered as the holotype by Orchymont (1926b)]; 1 female 1 male (IRSNB): “ Mt. Banahao / Luzon // Cotype // Pachysternum / curvatum // coll. d’Orchymont // Para- / type ”. The species was described twice: (1) a short Latin description lacking any data on type specimens was published by Orchymont (1925); (2) a detailed English description with precise citing of type specimens was published by Orchymont (1926b). The description published by Orchymont (1925) fulfills all requirements of the International Code of Zoological Nomenclature (ICZN 1999) and the paper is therefore correctly considered as the original description (see, e.g., Hansen 1999). However, the type material is not specified in this paper and no holotype is designated; all type specimens used for the description has to be therefore formally considered as syntypes. The subsequent designation of the holotype by Orchymont (1926b) is therefore invalid following Articles 73.1.3. and 72.4.1 of the Code (ICZN 1999). Hence, the lectotype of the species is designated herein: as the differences in male genitalia are crucial for the diagnosis of the species, we have chosen the single male available as the lectotype, irrespectively to the previous decision by Orchymont (1926b) to designate the female from Imugan as “the holotype ”.
Additional material examined: PHILIPPINES: Leyte: 1 spec. (FHGC): Visca, N of Baybay, elev. 200– 500 m [10°42'N 124°48.5'E], 1991, lgt. Schawaller. Luzon: 3 spec. (IRSNB): Mt. Makiling [14°8'4.5''N 121°12'30''E], without date, lgt. Baker; 3 spec. (FMNH): Laguna, Los Baños, elev. 300 m [14°10'N, 121°12'E], vi.1947, lgt. F. G. Werner; 598 spec. (FMNH, NMPC): Mt. Makiling, 4 km SE Los Baños, [14°8'17''N 121°14'22''E], 11.iv.1977, lgt. L. Watrous. Mindanao: 5 spec. (FMNH): E slope Mt. McKinley, Davao Province [=? Mt. Apo, close to Davao city, 7°6'N 125°24.5'E], ix.1946, lgt. H. Hoogstraal & D. Heyneman; 1 spec. (FMNH): same locality, 28.ix.1946, lgt. F. G. Werner; 1 male (IRSNB): Momungan [= Baloi, 8°6'54''N 124°13'19''E], without date and collector; 2 spec. (FMNH): Davao del Sur, Mainit river, Mt. Apo, elev. 1829 m [6°59'N, 125°16'E], 2.ix.1930, lgt. C. F. Clagg; 1 spec. (FMNH): Mainit, E slope of Mt. Apo, elev. 1311 m [6°59'N 125°16'E], xi.1946, without collector; 17 spec. (NHMW, NMPC): South Cotabato, Mt. Matutum, Tupi [6°21'28''N 125°4'18''E], ii.1996, lgt. Mohagan. Unknown location: 3 spec. (IRSNB): Tangrolan, Bukidnon, withoutdate, lgt. Baker.
Differential diagnosis. By the general coloration and continually arcuate outer margin of anterior tibiae rather easily distinguishable from all Pachysternum species except the some forms of P. apicatum, P. sandacanum from northern Borneo and P. haemorrhoum from eastern Palaearctic. Except for the fact that P. curvatum is the only species of the genus in Philippines and does not co-occur with any above species (as well as with any other species of Pachysternum), it may be distinguished from them by the shape of the median lobe of the male genitalia (gradually narrowing apicad and acute at the very apex (Fig. 37b–c), in contrast to blunt at very apex in P. apicatum, distinctly narrowed in apical fourth in P. sandacanum and widely expanded subapically in P. haemorrhoum). Pachysternum sandacanum also differs by smaller body size (2.6–3.3 mm in P. curvatum, 2.3–3.1 mm in P. sandacanum). Most specimens of P. apicatum may be distinguished by at least weakly sinuate or angulate outer margin of anterior tibiae (at least when seen in slightly different angles than dorsally; outer margin of anterior tibiae is continually arcuate in P. curvatum even when seen from slightly oblique angles). Pachysternum haemorrhoum also differs by the uniform microsculpture throughout the metaventrite (Fig. 21), in contrast to the highly microsculptured and densely pubescent metaventrite laterally of the femoral lines in P. curvatum (as in Fig. 20)
Redescription. Body widely oval, shape of elytra sexually dimorphic, female with distinctly pronounced humeral portion of elytra. Body length 2.1–3.3 mm (lectotype: 2.3 mm); body width 1.6–2.2 mm (lectotype 1.7 mm).
Coloration (Fig. 56). Clypeus reddish to dark brown, frons uniformly dark brown without apparently pale median portion. Pronotum dark brown, lateral margins only very vaguely and narrowly paler. Elytra brown to dark brown, except for pale reddish spot on apex of each elytron extending up to posterior fourth to third on intervals 2– 5. Ventral surface brown to dark brown, abdominal ventrites 1–4 brown with pale lateral portions, ventrite 5 entirely pale. Legs reddish brown.
External morphology. Clypeus with coarse and dense punctation consisting of uniform punctures. Frons with punctations similar to that on clypeus, punctures separated ca. 2–3× puncture diameter. Interstices without microsculpture. Larger punctures on pronotum rounded, much larger than small punctures, small punctures minute, scar-like, divided by 2–3× puncture width. Pronotal interstices without microsculpture. Prosternum with very distinct median carina. Elytral series consisting of large, shallow punctures; interval punctation with minute semicircular punctures much smaller than serial ones, interval punctation consisting of two slightly different sizes of punctures, larger punctures setiferous; interstices without any trace of microsculpture. Elytral series distinctly impressed. Preepisternal elevation of mesothorax with deep posterolateral pits. Femoral lines on metaventrite slightly angulate, median portion of metaventrite bearing moderately coarse but rather sparse setiferous punctation, interstices without microsculpture; lateral portions with very coarse and dense, densely pubescent punctation. Outer margin of anterior tibia continually arcuate, outer series of spines not interrupted.
Male genitalia (Fig. 37). Tegmen 1.1–1.2 mm long, median lobe 1.2–1.3 mm long. Phallobase ca. twice as long as parameres, bearing small, slightly asymmetrical basal manubrium. Median lobe widest at midlength, gradually narrowing apicad, apical portion triangular, acute at very apex; gonopore subapical, rather indistinct; lateral pubescent lobes narrow. Sternite 9 with widely rounded median projection, without apical emargination.
Variation. Slight variability was observed only in the extent of pale spots on elytra (Fig. 56) and in the coloration of the clypeus, which may be pale reddish to dark brown.
Biology. A long series of this species has been collected from “rotting figs” at Mt. Makiling by L. Watrous. Collecting circumstances of other specimens are unknown.
Distribution. Endemic to Philippines, known from islands of Luzon, Leyte and Mindanao.
Discussion. The species is rather similar to the some specimens of P. apicatum in all external characters including the presence of deep pits in posterolateral corners of the preepisternal elevation of the mesothorax (as in Fig. 18). Based on its vicariant distribution with P. apicatum, it may in fact even represent only a local population or subspecies of P. apicatum. However, the small differences in the shape of the apex of the median lobe of the aedagus and in the shape of the anterior tibiae support the status of P. curvatum as a separate species. Pachysternum curvatum is also very similar to P. sandacanum from northern Borneo in dorsal coloration and shape of anterior tibiae, but the differences in body size and in the shape of the median lobe between these species is very apparent and clearly supports the separate specific status of the populations in Philippines and in northern Borneo.
description: Published as part of Fikáček, Martin, Jia, Fenglong & Prokin, Alexander, 2012, A review of the Asian species of the genus Pachysternum (Coleoptera: Hydrophilidae: Sphaeridiinae), pp. 1-53 in Zootaxa 3219 on pages 25-27, DOI: 10.11646/zootaxa.3219.1.1, http://zenodo.org/record/280223