Sandracottus rotundus Sharp, 1882

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 rotundus Sharp, 1882

Figs 11 , 22 , 27 , 45 , 57

Sandracottus rotundus Sharp, 1882: 688 (type locality “ Celebes ” [ Indonesia, Sulawesi]); Régimbart 1899: 337 (descr.); Zimmermann 1920: 235 (cat.); Hájek and Nilsson 2024: 91 (cat.).

Type material.

Holotype: Male, “ Type H. T. ”, “ Celebes 985 rotundus ”, “ Sharp Coll. 1905-313 ” ( NHMUK). Examined.

Additional material.

(80 specimens): • Indonesia: 1 ex., “ INDONESIA, N-Sulawesi vic. Raja Basar b. Moutong, 15 m N 0 ° 29 ' 78 ” E 121 ° 12 ' 99 ”, 28. II. 2009, river valley (* 016 *), A. Skale leg. ” ( CAS); 2 exs., “ Minahassa, Celebes ” [Minahasa, Sulawesi] ( RMNH); 5 exs., “ Rosenberg, Toelabollo, Celebes ” [Tulabalo, Sulawesi] ( MNHN, RMNH); 1 ex., “ Indonesia, Celebes ” [Sulawesi] ( NHMUK); 1 ex., “ Indonesia, C-Sulawesi, 45 km SE Palu, 1994, 01 ° 11 ' S 120 ° 08 ' E, J. Haft leg. (5) ” ( NMW); 1 ex., “ Indonesia, Sulawesi Utara, Dumoga Bone N. P., XI. 1985, Rothamsted light trap, site 1, 200 m, H. Barlov leg. ” ( NHMUK); 1 ex., “ Indonesia, Sulawesi Utara, Dumoga Bone N. P., 17. I. 1985, lowland forest 200–300 m ”, “ R. Ent. Soc. London Project Walace B. M. 1985-10 ” ( NHMUK); 1 ex., “ Indonesia, Sulawesi Utara, Dumoga Bone N. P., 6. II. 1985, site 5, Tumpah transect, 300 m, J. D. Holloway leg. ” ( NHMUK); 1 ex., “ Indonesia, Sulawesi Togian Islands , Pulau Togian, river in forest south of Wakai , 5. - 17. VIII. 1987, D. T. Bilton leg. ” ( CLH); 16 exs., “ Sulawesi Togean Islands , Kadidiri Island interior, 30 m, 28. viii. 2011, 00 21.531 S 121 50.959 E (SUL 005) ” ( MZB, ZSM); 50 exs., “ Indonesia , C-Sulawesi, Togian Islands , Kaldidiri Island near Paradise Island Resort , 50 m, S 00 ° 21 E 121 ° 50, 12. - 15. II. 1997, J. Haft leg. ” ( CLH, CJS, NMB, NMPC).

Redescription.

Body broad oval, shiny, testaceous with black markings. Ventral side completely dark brown to black, legs testaceous, hind legs somewhat darker.

Head testaceous with posterior part and broadly so on posterior half alongside as well as two elongate spots on clypeus black, shiny (Figs 11 , 57 ). Surface almost smooth consisting of dense and very numerous punctures of different size and of larger, much sparser ones, particularly numerous on frons. Clypeal grooves, punctures alongside eyes and transverse depression beside eyes distinctly impressed, punctures large and coalescent. Antennae testaceous; antennomeres slender, antennomere V 4.5 × as long as broad.

Pronotum black with broad lateral testaceous markings (Figs 11 , 57 ). Surface very superficially shagreened, almost not visible, with dense punctation; punctures medium-sized mixed with smaller ones. Anterior and lateral puncture lines dense and coalescent, punctures becoming sparse towards middle and lacking in very middle of anterior margin. Posterior puncture line with coarse and coalescent punctures on middle of each side, distinctly smaller and spaced out on disc.

Elytra black with five testaceous markings, consisting of one basal, two lateral, one just behind middle, and one posterior apical one (Figs 11 , 57 ). Epipleura testaceous to ferrugineus brown. Surface very slightly and superficially shagreened and covered with double punctation, smaller and denser ones as well as larger much sparser ones. Puncture lines with groups of medium-sized punctures mostly grouped by five or six punctures; groups closer together on discal line.

Ventral side dark brown. Legs particularly fore and mid legs testaceous, hind legs ferrugineus brown to dark brown. Prosternal process short and broad, 1.3 × 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, complete surface densely covered with very small punctures and larger sparser ones. Posterior margins rounded, bordered with some large and coalescent punctures on middle of each side.

Measurements: TL = 12.4–12.8 mm, TL-h = 11.4–11.9 mm, TW = 7.6–7.9 mm.

♂. Protarsomeres I – III strongly enlarged with three larger suckers and numerous smaller ones. Mesotarsomeres I – III with two rows of smaller suckers. Median lobe of aedeagus in ventral view broad, constricted medially, parallel-sided in apical part up to apex, here slightly broadened and broadly rounded (Fig. 22 a ). Parameres broad and strongly pointed at apex, slightly longer than median lobe (Fig. 22 b ).

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

Differential diagnosis.

The species is well distinguished from all other Oriental species of the genus by its colouration and roundish oval body. From the dorsal colouration S. rotundus is near to the Australian S. bakewellii bakewellii (Figs 1 , 46 ) which is generally more elongated. Furthermore, both species can be separated by the shapes of their median lobes (Figs 12 a, b , 22 a, b ).

Distribution.

Indonesia: northern and central Sulawesi including Togian Islands (Fig. 27 ). Specimens were collected between 30 and 300 m a. s. l.

Habitat.

Sandracottus rotundus seems to be restricted to stagnant water bodies in primary lowland forests of northern and central Sulawesi and their adjacent islands. All specimens on Kaldiri Island were obtained from muddy forest pools (depths up to 30 cm) and from shallow water of a forest lake not far from the sea. According to Jan Haft (pers. comm. 1998) those pools were frequently used and probably created by Babirusas [ Babyrousa togeanensis (Sody, 1949) ] (Fig. 45 ). Co-occurring species include the rare Cybister aterrimus Régimbart, 1899 , Hydaticus species of the pacificus group, and some unidentified Copelatus .

Conservation.

A rare species recorded from a very restricted area in Indonesia. Most probably the species is associated with the declining primary lowland rainforests on the island Sulawesi. It is recommended to be listed in the next IUCN red list.

Figures

Figure 27. Distribution of Sandracottus femoralis [black dots] in New Guinea and the Moluccas, and S. rotundus [red squares] on Sulawesi.

Figures 8–11. Habitus of 8 Sandracottus insignis (Luzon, Philippines) 9 S. jaechi (paratype from Nuwara Eliya, Sri Lanka) 10 S. maculatus (Thailand) 11 S. rotundus (Sulawesi, Togian Islands).

Figures 20–22. Median lobe of aedeagus in ventral view (a), and right paramere in lateral view (b): 20 Sandracottus jaechi 21 S. maculatus and 22 S. rotundus.

Figures 43–45. Habitats of Sandracottus 43, 44 Malaysia, Sabah, Kinabatangan riv. 8. - 15. VI. 2003, Uncle Tan´s camp, habitat of S. maculatus (photos: J. Šťastný) 45 Indonesia, Sulawesi, Togian Islands, Kaldidiri Island near Paradise Island Resort, Babirusa puddles (on the left), habitat of S. rotundus (photo: J. Haft).

Figures 54–57. Habitus of 54 Sandracottus jaechi (holotype, Sri Lanka, Nuwara Eliya) 55 Sandracottus insignis (Philippines; Luzon, Los Banos) 56 S. maculatus (Borneo, Sabah, Sungai Kinabatangan) 57 S. rotundus (Indonesia, Sulawesi, Togian Islands, Kaldidiri Island).

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 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).

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.