Coelostoma (Holocoelostoma) stultum ( Walker, 1858 )

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 : 25-28

Coelostoma (Holocoelostoma) stultum ( Walker, 1858)

Fig. 10 A–M

Hydrobius stultus Walker, 1858: 209 .

Coelostoma stultum – Zaitzev 1908: 404 (catalogue). — Knisch 1924: 113 (catalogue).

Coelostoma (Holocoelostoma) stultum – Orchymont 1923b: 2 (faunistics); 1928: 56 (catalogue); 1936: 17 (faunistics). — Mouchamps 1958: 3 (transfer to Holocoelostoma ). — Satô 1979: 49 (faunistics). — Hebauer 2000: 6 (faunistics); 2002: 31 (faunistics); 2006: 8 (faunistics). — Darilmaz & Ahmed 2015: 10 (faunistics). — Jia et al. 2017: 118 (faunistics).

Differential diagnosis

Large species, easy to recognize from all other Coelostoma species except C. bhutanicum by the combination of the widely parallel-sided median lobe with apical gonopore and emarginate abdominal apex with stout setae. From C. bhutanicum it may be only recognized by the morphology of the median lobe of the aedeagus, which is wide basally, gradually narrowing to ca midlength and more less of the same width in apical half. In contrast to C. bhutanicum , C. stultum does not have strongly sclerotized lateral margins of the median lobe and the median lobe is not spoon-like in form.

Material examined

Lectotype (here designated)

SRI LANKA • ♀; “Ceylon”; [7º52ʹ23.80ʺ N, 80º46ʹ18.52ʺ E]; [243 m a.s.l.]; BMNH.

Other material

INDIA – Uttar Pradesh • 2 ♂♂; Fatapur Sikri [Fatehpur Sikri]; [27º5ʹ41.97ʺ N, 77º40ʹ4.89ʺ E]; [174 m a.s.l.]; 31 Oct. 1997; J. Šťastný leg.; NMPC . – Rajasthan • 1 ♂, 28 specs; Bharatpur, Keoladeo National Park and around ; 27º12.42ʹ N, 77º30.48ʹ E; 220 m a.s.l.; 31 Aug.–5 Sep. 2002; M. Fikáček and P. Šípek leg.; NMPC • 3 specs; same collection data as for preceding; NCBS-BL022–024 • 3 specs; same collection data as for preceding; UASB 01923080–82 • 2 specs; same collection data as for preceding; ZSI • 1 ♂, 3 specs; Bharatpur ; [27º12ʹ54.67ʺ N, 77º30ʹ10.80ʺ E]; [180 m a.s.l.]; 11 Aug. 1989; A. Riedel leg; NHMW . – Goa • 1 ♂; “ 30 km S of Margao (= Madgaon), Palolem env.; 15º00.47ʹ N, 74º01.58ʹ E ” [15º0ʹ38.37ʺ N, 74º1ʹ23.76ʺ E]; 0–20 m; 12–14 Aug. 2002; P. Šípek and M. Fikáček leg.; NMPC . – Assam • 1 ♂, 1 ♀; “ Kohora (Kaziranga village) at Green Reed hotel ; 26º35ʹ N, 93º26ʹ E ” [26º35ʹ21.81ʺ N, 93º24ʹ44.07ʺ E]; “ 160 m ” [1000 m a.s.l.]; 16–18 Apr. 2008; Fikáček, Podskalská and Šípek leg.; at light; NMPC . – Meghalaya • 1 ♂; W Garo Hills, Balphakram NP; 25º11ʹ N, 90º51ʹ E; 300–500 m a.s.l.; 22–27 May 1996; Jendek and Šauša leg.; NHMW • 1 ♂; W Garo Hills, Bagmara ; 25º11.5ʹ N, 90º38.5ʹ E; ca 100 m a.s.l.; 18–21 May 1996; Jendek and Šauša leg.; NHMW .

SRI LANKA • 1 ♂; Colombo ; [6º55ʹ40.52ʺ N, 79º51ʹ39.79ʺ E]; [13 m a.s.l.]; BMNH .

Published records

All published records of C. stultum from the Indian subcontinent need re-examination, as they very likely include misidentified C. bhutanicum .

Description

FORM AND COLOUR. Body length 3.8–5.2 mm, body width 2.6–3.3 mm. Body oval in dorsal view, moderately convex in lateral view. Head black; pronotum and elytra uniformly dark brown; ventral surface uniformly reddish brown. Tarsi pale brown. Mouthparts and antennae yellowish brown, antennal club brown.

HEAD. Dorsal punctation dense, consisting of simple punctures without associated ridges; trichobothria present; surface between punctures smooth. Anterior margin of clypeus arcuate. Eyes large, interocular distance ca 3.3× the width of one eye in dorsal view; eye emarginate anteriorly. Labrum moderately sclerotized, largely exposed anterior of clypeus. Antenna with 9 antennomeres, club loosely segmented. Second maxillary palpomere moderately broad.

PROTHORAX. Pronotum bisinuate anteriorly, anterolateral corners obtuse; posterior margin moderately bisinuate, posterolateral corners rectangular.Anterior and lateral margins with distinct bead not extending to posterior margin. Pronotal punctation sparser and finer than on head, consisting of simple punctures without associated ridges; surface between punctures smooth. Prosternum slightly projecting mesally on anterior margin, carinate mesally, anterior portion of carina very weakly elevated.

MESOTHORAX. Elytral punctation dense and moderately coarse, consisting of punctures without transverse ridges. Series of impressed punctures present along suture and laterally. Sutural stria weakly impressed, present in apical half. Mesoventral plate as long as wide, arrowhead-shaped, bluntly pointed anteriorly, posteriorly widely attached to metaventrite.

METATHORAX. Metaventrite raised medially, posterior third and anterior of median elevation bare, lateral portions 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 with sparsely arranged stout setae only; metafemur with very sparse pubescence.

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

AEDEAGUS ( Fig. 10 K–M). 0.8–1.0 mm long. Median lobe broad at base, slightly tapering towards apex; gonopore situated at apex but still directed dorsally, widely oval in shape. Parameres slightly longer than median lobe; apex rectangular at inner margin, not projecting inwards, rounded laterally. Phallobase small, wider than long.

Variation

The form of the median lobe differs slightly between the examined specimens from India and Sri Lanka and those from Taiwan and Japan (see Liu et al. 2020), but in all cases the median lobe is widest at the

base and narrowed ca at mid-length. Additional studies are needed to understand whether this variation may represent a geographic variability of the species.

Lectotype designation

On the request to loan the type specimens from the Walker collection at BMNH, we received two specimens, both considered as syntypes. Both are females, but each of them belongs to a different species: the specimen labelled as cotype belongs to the subgenus Holocoelostoma based on the emarginated abdominal apex and mesofemora lacking dense pubescence; it agrees externally in all details with a male specimen from Colombo, the genitalia of which are illustrated on Fig. 10M . The second specimen, labelled as type, has an emarginate abdominal apex and densely pubescent mesofemora, and hence belongs to the subgenus Lachnocoelostoma . To fix the current concept of C. stultum and of Holocoelostoma (of which C. stultum is the type species), we are therefore designating the first specimen as the lectotype.

Biology

Aquatic species; in Japan and Taiwan it inhabits vegetation-rich places with muddy bottoms, typically ponds, rice fields and river sides ( Liu et al. 2020; Nakajima et al. 2020).

Distribution

Coelostoma stultum is reported as a very widespread species, extending from the Arabian Peninsula ( Fikáček et al. 2010) to Japan ( Hayashi 2008) and New Guinea ( Hebauer 2001) (see Hansen 1999 for a summary), also recorded from the Mascarene Islands and Madagascar ( Hebauer 2006). This distribution is, however, surely partly based on misidentified specimens of C. bhutanicum , and needs revision. Based on the material examined for this study and published illustrations of male genitalia, we may confirm the species to occur in the following countries at present: United Arab Emirates ( Fikáček et al. 2010), India (this paper), Srí Lanka ( Walker 1858, this paper), Taiwan ( Liu et al. 2020) and Japan ( Hayashi 2008).

Figures

Fig. 10. Coelostoma (Holocoelostoma) stultum (Walker, 1858). A. Dorsal habitus. B. Lateral habitus. C. Head. D. Thorax in ventral view. E. Dorsal punctation of head. F. Dorsal punctation of pronotum. G. Dorsal punctation of elytron. H. Abdominal ventrites. I–J. Detail of abdominal apex. K–M. Aedeagus: dorsal (K) and ventral (L–M). N. Labels of the lectotype. Specimens: A–I, K–L. Non-type specimens from Uttar Pradesh, Fatehpur Sikri, ♂ (NMPC). J, N. Lectotype, ♀ (BMNH). M. Non-type specimen, ♂, from Sri Lanka: Colombo (BMNH).