A taxonomic review of the Gyrinidae (Coleoptera) in Korea

Abstract A taxonomic review of Korean Gyrinidae is presented. Seven species [Dineutus orientalis (Modeer, 1776), Gyrinus gestroi Régimbart, 1883, Gyrinus japonicus Sharp, 1873, Gyrinus pullatus Zaitzev, 1908, Orectochilus punctipennis Sharp, 1884, Orectochilus Regimbarti Sharp, 1884 and Orectochilus villosus (Müller, 1776)] in three genera are recognized, one of which (Orectochilus punctipennis Sharp, 1884) is reported for the first time in Korea. We also found that Gyrinus curtus Motschulsky, 1866 previously recorded in Korea was an incorrect identification of Gyrinus pullatus Zaitzev, 1908. Habitus and SEM photographs, distribution maps, keys, and diagnoses of genera and species are provided.


Introduction
The Gyrinidae are water beetles with unique swimming behavior where adults rapidly gyrate and whirl on the surface of water. They inhabit stagnant or slowly running water and prefer clean oxygen-rich habitats (Brinck 1955). Members of the Gyrinidae are characterized by the combination of the following characters: compound eyes divided completely with one pair on the dorsal surface of the head (above the water line) and another on the ventral surface of the head (below the water line); antenna short with a broad, cup-shaped scape, subtriangular pedicel, elongate but compact flagellum; middle and hind legs broadly expanded and fringed with setae for swimming (Miller and Bergsten 2012).
The whirligig beetles contain about 1000 species in 25 genera worldwide (Slipinski et al. 2011) and 118 species in seven genera in the Palaearctic region (Mazzoldi 2003). In Korea, seven species in three genera have been recorded (Jung et al. 2011), 50 species in six genera from China, 16 species in three genera from Japan and 11 species in three genera from the Far East of Russia (Mazzoldi 2003).
It was Kolbe (1886) who recorded the first gyrinid species, Gyrinus japonicus Sharp, 1873 in Korea. About 50 years later, Japanese entomologists, Takizawa (1931) and Kamiya (1936) reported two species (Dineutus orientalis Modeer, 1776 andG. japonicus Sharp, 1873) with descriptions and illustrations. Cho (1957) was the first Korean beetle taxonomist who studied Korean gyrinid fauna in detail. Since then, a few entomologists have studied Korean gyrinid beetles, mainly in the local fauna and no taxonomic review has been performed since Yoon (1988). Accordingly, this review is an updated contribution worth undertaking for Korean Gyrinidae.
Habitat. Most Korean specimens are found in ponds or mountain streams with plentiful vegetation and low water temperature. Some specimens were collected in ponds near brackish water.
Habitat. All specimens were collected in ponds with plentiful vegetation in Jejudo Island. They are frequently found together with D. orientalis or G. japonicus.
Diagnosis. Length 6.5-8.5 mm. Ventral surface mostly black; mouthparts, prosternum, legs, sternite VIII brown to reddish brown; hypomera, epipleura dark brown. Ligula with a row of compact spines on antero-medial part. Anterior margin of mesoventrite acute and posterior margin bifid; shallow pit (arrow in Fig. 26) and vertical plica present on postero-medial part; shallow plica present on antero-lateral parts. Metepisternum with a pit (arrow in Fig. 27) and shallow groove on anterior part. Sternite II with small pit and transverse plica on anterior part (arrow in Fig. 28). Median lobe of aedeagus (Figs 47-49) parallel-sided at middle to apex, shorter than paramere, narrowest at middle; apical margin nearly straight; sperm-groove as in Fig. 48. Paramere as in Figs 47 and 49.
Diagnosis. Length 6.0-7.0 mm. Ventral surface mostly reddish brown; ventral part of antennomere 2, mouthparts, prosternum, legs, posterior part of sternite VII, sternite VIII yellowish brown to brown; hypomera, epipleura yellowish brown. Ligula with a row of sparse spines on antero-medial part. Anterior margin of mesoventrite rounded and posterior margin bifid; deep pit (arrow in Fig. 29) and vertical groove present on postero-medial part; deep groove present on antero-lateral parts. Metepisternum with a deep pit (arrow in Fig. 30) on anterior part. Sternite II with pit, transverse and thick plica on anterior part (arrow in Fig. 31). Median lobe of aedeagus (Figs 50-52) narrowed apically, shorter than paramere; narrowest at anterior fifth; apical margin nearly straight; sperm-groove as in Fig. 51. Paramere as in Figs 50 and 52.
Distribution. Korea, Japan, Russia (Far East) (Mazzoldi 2003). Remarks. Orectochilus punctipennis is recorded for first time in Korea. This species can be distinguished from O. regimbarti by the small size (less than 7.0 mm) and median lobe of aedeagus shorter than paramere. It also differs from O. villosus by the black body, posterior margin of the elytron acute, paramere curved at middle and apical margin of gonocoxa (Fig. 56) rounded.
Habitat. A single female specimen was collected near the margin of a stream with plentiful vegetation and slow flow velocity.
Remarks. This species has been recorded in Korea by Kwon and Suh (1986), Kim et al. (1994) and Cho and Park (2010), only in their checklists without any taxonomic comments and specimens. We could not find any Korean specimens and the occurrence of this species in Korea is suspicious. However, its occurrence in Korea is possible because it is known from Japan and Russia (Far East). Published Korean records. Orectochilus villosus: Yoon (1988: 615); Kim et al. (1994: 134); Cho and Park (2010: 96).