Megadytes (Bifurcitus) ducalis Sharp, 1882

Hendrich, Lars, Manuel, Michael & Balke, Michael, 2019, The return of the Duke - locality data for Megadytes ducalis Sharp, 1882, the world's largest diving beetle, with notes on related species (Coleoptera: Dytiscidae), Zootaxa 4586 (3), pp. 517-535 : 518-523

Megadytes (Bifurcitus) ducalis Sharp, 1882

Megadytes ducalis Sharp, 1882: 713 (orig. descr.); Zimmermann 1920: 256; Blackwelder 1944: 80. Megadytes (Bifurcitus) ducalis Sharp, 1882 ; Brinck 1945: 8; Trémouilles 1989b: 153; Miller & Bergsten 2016: 108; Nilsson & Hájek 2019: 80.

Type locality. Brazil .

Type material examined. Holotype , male (BMNH): " Brazil, Saunders ", " Type ", " Megadytes ducalis Sharp ".

Other material examined. Brazil: 1 male, 1 female, " San Antônio da Barra [= Condeúba, City Center is at - 14.899° -41.968°, 660 m], Prov. de Bahia, Brésil" ; 1 female, " S. Antonia da Barra pr. de Bahia Gounelle 11.12.1888 " [printed label] ; 1 female, "S. Antonia da Barra pr. De Bahia CH Pujol 1890" [printed label] (MNHN- CR, drawer 60) ; 1 female, " Bahia Brésil " ; 1 male, "S. Antonia da Barra Pr. de Bahia Gounelle 11.12.1888 " [printed label] ( MNHN-CG, drawer 92) ; 1 male, "Museum Paris Brésil Coll. E. Gounelle 1915" [green printed label]

[among indet. material in separate drawer]; 1 female, " Brésil Bahia intr" [printed label], " ducalis Sharp " [handwritten label] ( MNHN-CW) ; 1 female " Cybister giganteus Brésil " [handwritten label] ; 1 female, "Museum Paris Brésil Coll. E. Gounelle 1915" [green printed label], " Megadytes ducalis Shp. San Antonio da Barra " [handwritten label] (MNHN-Magasin) .

Descriptive notes. Large beetle (TL> 42.9 mm) of very robust and "thick" appearance ( Fig. 2A ). Descriptions of this species, based on the male holotype, were provided by Sharp (1882) and Trémouilles (1989). Here we provide photos of the habitus ( Figs 1A, D , 2A , 3 ) and focus on morphological characters of the male in different views ( Figs 7 A–E).

The median lobe, with both parameres, of a male from Coll. Guignot is figured in ventral view ( Fig. 4A ), the anterior half of the median lobe in lateral view ( Fig. 4B ) and the tip of the median lobe in dorsal view ( Fig. 4C ). The median lobe of the holotype is presented in Fig. 4D . It appears much broader than in the other specimens we studied. This is apparently due to manipulation by previous researchers, perhaps J. Balfour-Browne, whereby cardboard wedges were inserted in between the main lobe and the ventral sclerite to expose the latter. This is actually seen in several other Megadytes specimens in the BMNH collection, and can lead to significant changes to the shape of the median lobe.

Female. No traces of elytral striae or any other kind of sexual sculpture on pronotum or elytra. Without protarsal disks and yellow setae on ventral surface of mesotarsomere I; otherwise no external difference with male. Broadest part of femur in hind legs 5.3 mm ( Figs 1A , 7E ).

Measurements, holotype: TL = 47.2 mm; TL-H = 44.1 mm; TW = 26.4 mm. Additional specimens, males: TL = 42.9–47.0 mm; TL-H = 41.3–43.8 mm; TW = 25.1–25.9 mm. Females. TL = 43.5–47.4 mm; TL-H = 40.7– 44.1 mm; TW = 24.0–26,1 mm.

Note. The largest known specimen of M. ducalis (female, TL= 47.4 mm) is deposited in the collection of Maurice Régimbart in the Muséum National d'Histoire Naturelle in Paris ( Fig. 3 ).

Distribution. Only known from Condeúba, Bahia, Brazil ( Fig. 11 ).

Habitat. Unknown.

Figures

FIGURE 1. Habitus in dorsal view of: A) M. ducalis, B) M. lherminieri, C) M. magnus; habitus in ventral view of: D) M. ducalis, E) M. lherminieri (Ecuador, Esmeraldas), F) M. magnus (Paraguay, Cerro Lambaré).

FIGURE 2. Habitus in lateral view of: A) M. ducalis, B) M. lherminieri, C) M. magnus.

FIGURE 3. Female of M. ducalis from collection Régimbart in MNHN [TL = 47.4 mm], the largest known diving beetle specimen in the world: "San Antônio da Barra, Prov. de Bahia, Brésil".

FIGURE 4. Megadytes ducalis, male specimen from collection Guignot: A) median lobe with parameres in ventral view, B) tip of median lobe in lateral view, C) anterior half median lobe in ventro-apical view; Megadytes ducalis, holotype: D) median lobe in ventral view (Foto: R. Angus). Scale bars = 1.5 mm.

FIGURE 7. Megadytes ducalis, male from collection Guignot: A) frontal view, B) ventral view of head and protarsus, C) left middle leg, D) dorso-lateral view of left side of head, pronotum and elytral base, E) ventro-lateral view of left hind leg. Scale bars = 5 mm.

FIGURE 11. Distribution of the subgenus Bifurcitus in Central and South America: White line: distribution of M. lherminieri; black line: distribution of M. magnus; red spot: only known locality for M. ducalis.