Dineutus (Rhombodineutus) chalybeus Zimmerman, 1924

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 : 58-60

Dineutus (Rhombodineutus) chalybeus Zimmerman, 1924

Fig. 4

Dineutes sinuaticollis Zimmerman, 1924: 3 .

Dineutus (Rhombodineutus) sinuaticollis: Ochs, 1926: 140 .

Material examined. PAPUA NEW GUINEA, Gulf Prov.: 1 male, Kikori River basin, Lubu River, below falls nr. Omo, 50 m., 6°58'41"S, 144°18'15"E, water temp. 19° C., 1 March 1995, 09:00-12:00 hrs., CL 7002, D. A. Polhemus ( USNM). 2 males, 5 females, Lakekamu River basin, Ivimka Creek along Kakoro Track, SE of Ivimka Research Station, 30 m., 7°44'20"S, 146°30'06"E, water temp. 25° C., 17 January 2001, 07:30–13:00 hrs., CL 7149, D. A. Polhemus ( USNM).

Discussion. This species has remained poorly known since its description by Zimmerman (1924). The holotype was a male specimen from “Jule Island”, a locality that Brinck (1983) considered “erroneous”, also noting that “No recent material is known.” Several series of Dineutus recently collected in the Kikori and Lakekamu river basins of southern Papua New Guinea, however, key to this species in Brinck’s (1983) key, and the shape of the posterior elytral margin matches his Fig. 60 for this species. One of the localities from which these recent series came is not far from Yule Island, an early settlement on the south coast of New Guinea, and it seems likely that the original type locality of “Jule Island” is an incorrect emendation of this place name.

Table 1: Ecological information for selected species of Gyrinidae occurring on New Guinea and Timor ___________________________________________________________________________________________________________ Species Recorded Elevational Recorded Water

Range* TemperatureRange** _____________________________________________________________________________________________________ NEW GUINEA

PORRORHYNCHUS

Subgenus Rhomborhynchus

TIMOR

Subgenus Dineutus

Dineutus regimbarti regimbarti 685–1460 m. 19.0–24.0 °C. _____________________________________________________________________________________________________

* includes elevational data from the references listed in the Literature Cited as well as recent observations. ** water temperatures are rounded to half degree increments, due to variation in measurement techniques used to acquire this data over the time series of the collections involved.

Presuming that these specimens have been correctly identified as this species, it indicates that D. chalybeus occurs in the lowland coastal and premontane forests of southern Papua New Guinea bordering the Papuan Gulf ( Fig. 4 ), an area not commonly visited by collectors. This would also account for the absence of captures from elsewhere on the island. In many respects D. chalybeus is similar to D. tetracanthus Régimbart , but the middle spine on the posterior elytral margin is angulate rather than acuminate as in the latter species.

The Ivimka Creek locality where this species was taken was a moderately swift, very clear, gravel bottomed stream, heavily shaded by primary rain forest with very large trees growing on nearly flat alluvial lowland terrain. This species was also encountered on the Omo River in the Kikori River Basin, where it was syntopic with Porrorhynchus (Rhomborhynchus) depressus depressus ; for a description of the Omo locality see the discussion under the latter species. Based on known collections, this subspecies occupies the Papuan Gulf Foreland and South Papuan Peninsula Foreland areas of freshwater endemism (Areas 25 and 30 respectively) as defined by Polhemus & Allen (2007).

This is the species listed as “ Dineutes (Rhombodineutus) sp. undet.” in Table 3 of Polhemus (1995).

Figures

FIGURE 4. Distribution of certain Dineutus (Rhombodineutus) species and subspecies on New Guinea. Symbols with grey centers represent previous records; symbols with black centers represent new records presented in this paper.