Dineutus (Dineutus) regimbarti regimbarti Régimbart, 1882

Polhemus, Dan A., 2011, New distributional records for Gyrinidae (Insecta: Coleoptera) on New Guinea and nearby islands, with a checklist of the New Guinea species, Zootaxa 2900, pp. 51-68 : 65

Dineutus (Dineutus) regimbarti regimbarti Régimbart, 1882

Dineutes Regimbarti Régimbart, 1882: 61 . Dineutus regimbarti: Ochs, 1959: 19 .

Material examined. EAST TIMOR, Ainaro Dist.: 1 male, 5 females, Eralisau River at bridge on road to Ainaro, 18 road km. S. of Maubisse, 1400–1460 m. [4600–4790 ft.], 8°53'48"S, 125°35'24"E, water temp. 19–19.5 °C., 12 November 2003, 08:30–09:30 hrs., CL 7266, D. A. Polhemus ( USNM); 5 males, 7 females, Saru River below road to Ainaro, 1 km. SW of Maubisse, 1240–1285 m. [4065–4220 ft.], 8°50'15"S, 125°35'32"E, water temp. 20 °C., 2 September 2004, 12:30–15:30 hrs., CL 7312, D. A. Polhemus ( USNM, BPBM). INDONESIA, Nusa Tenggara Timur Prov., Timor: 3 males, 4 females, spring and stream at Oe Hala, 10 km. N. of Soe, 685 m. [2250 ft.], water temp. 24° C., 11 Sept. 1991, CL 2593, D. A. and J. T. Polhemus ( BPBM).

Discussion. This large, ovate taxon, one of the largest Dineutus species in the world, is endemic to the mountains of Timor, has been rarely collected over the past 70 years, and is poorly represented in major collections. Previous records from Timor with minimal data were provided by Régimbart (1881) and Ochs (1937).

The Eralisau River collection locality was a clear, steeply dropping stream descending rapidly off the southern flank of the central Timorese mountains in a bed of tilted limestone bedrock and boulders. The stream channel was mostly open, consisting of cascades over sloping bedrock sheets, with deep pools below, and was mostly unshaded, with the surrounding hillsides having been cleared by burning, and grazing by water buffalo. The gyrinids were most abundant in a shaded pool formed beneath a high bridge on the road running from the hill station of Maubisse south to the lowland town of Ainaro. In western Timor, this species was also encountered on a deep, shaded pool at the head of Oe Hala spring, which emerges from a limestone plateau north of the town of Soe.

The derivation of the unusual doubly repetitive quadrinomial for this species, and its attribution, are worthy of explanation. A description of the Timorese taxon was originally prepared by Conrad Ritsema, who intended to name the species after Régimbart. Ritsema subsequently allowed Régimbart to publish it as part of a larger work by the latter author in the Notes from the Leyden Museum, but insisted the patronym be retained in Régimbart’s honor. Régimbart (1882) therefore added “(Ritsema in litt.)” after the species name, and noted that “I have retained the name of Regimbarti for this beautiful species for the sole reason that Mr. Ritsema has strongly insisted upon my doing so…” This created the combination Dineutus regimbarti Régimbart. Subsequently , Dineutus was divided into multiple subgenera, but this species remained in the nominate subgenus, leading to the combination Dineutus (Dineutus) regimbarti Régimbart. Finally, Ochs (1953) described another subspecies of D. regimbarti from the island of Sumba, D. regimbarti sumbaensis , thus making the Timorese taxon the nominate subspecies: Dineutus (Dineutus) regimbarti regimbarti Régimbart.