Coelostoma (s. str.) fallaciosum Orchymont, 1936

Sheth, Sayali D., Ghate, Hemant V. & Fikáček, Martin, 2020, Review of Coelostoma of the Indian subcontinent (Coleoptera: Hydrophilidae) Part 1: Coelostoma s. str. and Holocoelostoma, European Journal of Taxonomy 690, pp. 1-32 : 9-12

Coelostoma (s. str.) fallaciosum Orchymont, 1936

Fig. 4 A–K

Coelostoma fallaciosum Orchymont, 1936: 19 .

Coelostoma (s. str.) fallaciosum – Hansen 1999: 244 (assigned to Coelostoma s. str.). — Hebauer 2002: 28 (faunistics); 2006: 8 (faunistics).

Differential diagnosis

Among Indian Coelostoma without pubescent mesofemora, C. fallaciosum may be recognized by its relatively large body size (resembling that of C. stultum and C. bhutanicum ), simple abdominal apex without emargination or stout setae (with emargination and stout setae in both latter species) and with a typical aedeagus with subapical gonopore and strongly asymmetrical apex of the paramere. In the morphology of male genitalia it also resembles C. aeneolum ; see under that species for diagnosis.

Material examined

Holotype

INDONESIA • ♂; “ Br North Borneo , Mt. Marapok, Dent Province ”; [1º01ʹ15.25ʺ N, 114º33ʹ17.46ʺ E]; [694 m a.s.l.]; “ Collector G. leg.”; IRSNB.

Other material

INDIA • 2 ♂♂; “ Uttar Pradesh, Fatepur Sikri ” [Fatehpur Sikri]; [27º05ʹ41.97ʺ N, 77º40ʹ4.89ʺ E]; [174 m a.s.l.]; 21 Oct. 1997; J. Štastný leg.; NMPC .

NEPAL • 1 spec.; Annapurna , Pokhara, W of Phewa river + lake; [28º15ʹ50.88ʺ N, 83º58ʹ18.66ʺ E]; 800–850 m a.s.l.; 14–15 Oct. 2003; J. Schmidt leg.; NMPC .

Published records

NEPAL: Bheri Prov., Nepalgunj, 28º02ʹ59ʺ N 81º36ʹ56ʺ E ( Hebauer 2002); Annapurna Prov., Pokhara, W of Phewa river and lake ( Hebauer 2006).

Redescription

FORM AND COLOUR. Body length 5.6–6.4 mm (holotype 5.7 mm), body width 3.0– 3.6 mm (holotype 3.3 mm). Body oval in dorsal view, moderately convex in lateral view. Head black, pronotum and elytra dark brown to black with slightly paler margins; ventral surface uniformly dark brown, abdomen with pale spot at sides of each ventrite; appendages paler distally; mouthparts and antennal club brown.

HEAD. Dorsal punctation moderately dense, consisting of simple punctures without associated ridges; surface between punctures smooth; few trichobothria present. Anterior margin of clypeus arcuate. Eyes large, interocular distance ca 4 × the width of one eye in dorsal view; eye emarginate anteriorly. Labrum moderately sclerotized, largely exposed anterior of clypeus, dark brown dorsally, sinuate on anterior margin. Antenna with 9 antennomeres, club loosely segmented. Second maxillary palpomere moderately broad.

PROTHORAX. Pronotum bisinuate anteriorly, anterolateral corners obtuse; posterior margin almost straight, posterolateral corners rounded. Anterior and lateral margins with distinct bead not extending to posterior margin. Pronotal punctation moderately dense, slightly coarser than on head, consisting of simple punctures without associated ridges; surface between punctures smooth. Prosternum straight on anterior margin, weakly carinate mesally, anterior portion of carina not raised.

MESOTHORAX. Elytral punctation moderately dense and coarse, similar to that on pronotum, consisting of punctures without transverse ridges. Series of punctures absent. Sutural stria weakly impressed, present in apical two thirds. Mesoventral plate 1.1× as long as wide, arrowhead-shaped, bluntly pointed anteriorly, posteriorly widely attached to metaventrite.

METATHORAX. Metaventrite raised medially, median elevation bare, remaining median surface with sparse regular setae; lateral portions densely pubescent. Anterior metaventral process narrowly projecting between mesocoxae; posterior process bifid. Wings well-developed (macropterous).

LEGS. Profemur with dense pubescence except in apical fifth; mesofemur and metafemur with sparsely arranged short setae only.

ABDOMEN. All ventrites densely pubescent. First ventrite without carina. Posterior margin of last ventrite entire, without stout spines mesally.

AEDEAGUS ( Fig. 4 J–K). 1.0 mm long. Median lobe triangular, broad at base, tapering towards apex, bluntly rounded at apex; gonopore situated near apex, widely rounded. Parameres slightly longer than median lobe; pointed at apex, sinuate on outer margin. Phallobase small, slightly longer than wide.

Biology

Aquatic species, in Japan and Taiwan reported to inhabit shallow, well-vegetated pools ( Liu et al. 2020; Nakajima et al. 2020). The biology of the specimens from the Indian subcontinent is unknown; all examined specimens were collected at light.

Distribution

A widespread species, so far recorded from Nepal ( Hebauer 2002, 2006), northern India (this paper), Vietnam ( Hansen 1999), southern China ( Jia et al. 2014), Taiwan ( Jia et al. 2014; Liu et al. 2020), Japan

(Ishigaki and Iriomote Isl.; Hayashi 2008; Nakajima et al. 2020), Singapore ( Hendrich et al. 2004), Borneo (Orchymont 1936) and Sumatra ( Hansen 1999). First report for India.

Figures

Fig. 4. Coelostoma (s. str.) fallaciosum Orchymont, 1936, ♂ specimen from India: Fatepur Sikri (NMPC). A. Dorsal habitus. B. Lateral habitus. C. Head in dorsal view. D. Thorax in ventral view. E. Dorsal punctation of head. F. Dorsal punctation of pronotum. G. Dorsal punctation of elytron. H. Abdominal ventrites. I. Detail of abdominal apex. J–K. Aedeagus: ventral (J) and dorsal (K).