Sandracottus bizonatus Régimbart, 1899

Hendrich, Lars & Brancucci, Michel, 2025, Revision of the Oriental and Australasian diving beetle genus Sandracottus Sharp, 1882 (Coleoptera, Dytiscidae, Dytiscinae), ZooKeys 1223, pp. 87-147 : 87-147

Sandracottus bizonatus Régimbart, 1899

Figs 2 , 13 , 24 , 48

Sandracottus bizonatus Régimbart, 1899 a: 336 (type locality Malaysia, Sabah); Zimmermann 1920: 234 (cat.); Hájek and Nilsson 2024: 91 (cat.).

Type material.

Lectotype (herewith designated): Male, “ Borneo Sandakan Windrath ” [white printed label], “ bizonatus Reg. ” [handwritten label by Régimbart], “ Lectotype Sandracottus bizonatus Régimbart Hendrich & Brancucci des. ” [red printed label] ( MNHN). Examined.

Additional material.

(45 specimens): Malaysia. • Sabah: 1 ex., “ Borneo, Sabah Ranau, 4. v. 2006 Steven Chew NHMUK 2006-36 ” ( NHMUK); 1 ex., “ E. Malaysia, Sabah Borneo , Mt. Trus March-April 2010 Local leg. ”, “ coll. A. Skale Hof / Germany ” ( CAS); 5 exs., “ Nord Borneo Mt. Kina-Balu 5. VIII. 1903 John Waterstradth ” ( MNHN); 2 ex., “ Kinabalu Borneo ” ( MNHN); 1 ex., “ N. Borneo, Kinabalu ” ( MNHN); 8 exs., “ v. d. Does de Beye , Malakka ” ( RMNH); 1 ex., “ Borneo, H. E. Andrewes Bequest. B. M. 1922-221 ” ( NHMUK); 1 ex., “ Kina Balu ” ( MNHN); 2 exs., ” N. Borneo Mt. Kina Balu 5. VIII. 1903 J. Waterstradt leg. ” ( MNHN); 1 ex., “ Borneo , Sabah Mt. Kinabalu 3000 f, 21. IV. 1929 ex H. M. Pendlbury Collection ” ( CGW); 1 ex., “ Borneo Kinabalu 1500 m H. Bolle Berlin SW 11 ” ( MNHN); 1 ex., “ Borneo, Sabah, Tibow, 45 km NE of Sapulut, 600-900 m, 7. - 15. IV. 2000, Bolm leg. ” ( NMB); 1 ex., “ Borneo, Sabah, Kampung Pisang, Pisang env., tributary of Kuamut river , 29. VI. 1998, J. Kodada & F. Ciampor leg. ” ( NMW); 1 ex., “ Sabah, Borneo env. Keningau V. 1993 ” ( CLH); 2 exs., “ Nord Borneo ”, “ Samml. A. Zimmermann ” ( ZSM); 2 exs., “ Kinabalu Nord Borneo ”, “ Samml. A. Zimmermann ” ( ZSM); 5 exs., “ Kinabalu Borneo 1500 m ”, “ Samml. A. Zimmermann ” ( ZSM); 1 ex., “ Nordost Borneo Gebrüder W. Müller Vermächtnis 1909 ” ( SMTD); 1 ex., without locality label, “ Sandracottus bizonatus Gschwendtner det. ” ( SMTD). • Sarawak: 1 ex., “ Sarawak, Kapit distr., Rumah Ugap vill., Sut river , 3. - 9. III. 1994, J. Horák leg. ” ( NMW); 4 exs., “ Sarawak, Bario env., Pa Ukat, 24. VI. 2003, J. Šťastný lgt. ” ( CJS); 2 exs., “ Sarawak, Kelabit, Bario env. 21. - 25. VI. 2003, J. Šťastný lgt. ” ( CJS).

Redescription.

Body broad oval, shiny, reddish brown with broad black markings on elytra (Figs 2 , 48 ). Ventral side completely dark brown to black, legs testaceous, hind legs somewhat darker.

Head ferrugineus with posterior part broadly black, shiny. Black band protruding forwards to frons. Surface almost smooth consisting of dense and very numerous punctures of different sizes and of larger, much sparser ones, particularly numerous on frons. Clypeal grooves, punctures alongside eyes and transverse depressions beside eyes distinctly impressed, punctures large and coalescent. Antennae ferrugineus; antennomeres slender, fifth 4 × as long as broad.

Pronotum ferrugineus with large median black marking reaching from posterior to anterior margins (Figs 2 , 48 ). Surface shagreened, with dense punctation; punctures medium-sized mixed with smaller ones. Anterior and lateral puncture rows dense and coalescent, punctures becoming sparse towards middle and lacking in very middle of anterior margin. Posterior row of punctures with coarse and coalescent punctures in middle of each side, distinctly smaller and spaced on disc.

Elytra ferrugineus brown with black and broad markings consisting of three transverse bands (Figs 2 , 48 ); an antemedian one, a postmedian one and a preapical one. Epipleura ferrugineus brown. Surface of elytra very slightly and superficially shagreened and with double punctation, a smaller and dense punctation as well as a larger one much more sparsely distributed. Row of punctures with groups of medium-sized punctures mostly grouped in five or six punctures, groups closer together on discal row.

Ventral side dark brown. Fore and mid legs particularly testaceous, hind legs ferrugineus brown to dark brown. Prosternal process short and broad, 1.5 × longer than broad, flattened finely but distinctly sculptured; posterior margin broadly rounded. Whole surface very superficially shagreened and finely punctured. Metatibia with sparse medium-sized punctures on outer half. Ventrites II – VI very superficially shagreened, slightly and longitudinally wrinkled on lateral parts, on whole surface densely covered with very small punctures and larger and sparser ones. Posterior margins rounded, bordered with some large and coalescent punctures in middle of each side.

Measurements: TL = 12.5–13.0 mm, TL-h = 11.4–12.2 mm, TW = 8.5–9.0 mm.

♂. Protarsomeres I – III strongly enlarged with three larger suckers and numerous smaller one. Mesotarsomeres I – III with two rows of small suckers. Median lobe of aedeagus, in ventral view, broad, parallel-sided up to apex where it is slightly broadened and broadly rounded (Fig. 13 a ). Parameres broad, same length as median lobe, and pointed at apex (Fig. 13 b ).

♀. Similar to male, tarsi not enlarged. Microsculpture on ventrite VI as in male.

Differential diagnosis.

The combination of dorsal colour pattern (Figs 2 , 48 ) and shape of median lobe of aedeagus and parameres (Fig. 13 a, b ) separates S. bizonatus from all other species of the genus. The species is endemic to Borneo and co-occurs with S. maculatus .

Distribution.

Malaysia (Sabah, Sarawak) (Fig. 24 ). The eight specimens deposited in RMNH from Malacca are most probably mislabelled. According to a photo on a website from an insect dealer in Indonesia, the species was also collected in Kalimantan (https://www.giradis-insect.com/ 27.9.2024). Specimens were collected between 300 and 1.500 m a. s. l.

Habitat.

Muddy and shaded forest pools, rich in rotten leaves and more permanent side pools of larger forest streams in primary rainforests, partly shaded and enriched with rotten leaves and twigs (J. Kodada and J. Šťastný, pers. comm. March 2013).

Conservation.

A rare and highly endemic species of Borneo, probably associated with the declining primary lowland and hilly rainforests on the island (see Southeast Asian species S. femoralis , S. insignis , S. maculatus and S. rotundus ). Most records are from the end of the 19 th and the beginning of the 20 th century. According to present knowledge it is an endangered species. It is recommended to be listed in the next IUCN red list.

Figures

Figure 24. Distribution of Sandracottus bizonatus [red squares] and S. maculatus [black dots] in Southeast Asia.

Figures 1–3. Habitus of 1 Sandracottus bakewellii bakewellii (Northern Territory, Australia) 2 S. bizonatus (Borneo, Sabah, Kinabalu) 3 S. chevrolati (Sumba Island, Indonesia).

Figures 12–15. Median lobe of aedeagus in ventral view (a), and right paramere in lateral view (b) 12 Sandracottus bakewellii bakewellii 13 S. bizonatus 14 S. chevrolati and 15 S. dejeanii.

Figures 46–49. Colouration and habitus of 46 Sandracottus bakewellii bakewellii (Australia, Northern Queensland, Atherton Tableland, Mareeba) 47 S. bakewellii guttatus (Australia, Northern Territory, Ormiston Gorge) 48 S. bizonatus (Borneo, Sabah, Keningau) 49 S. chevrolati (Indonesia, Sumba Island, Waingapu).