Polypedilum (Pentapedilum) convexum ( Johannsen, 1932 )

Yamamoto, Nao, Hirowatari, Toshiya & Yamamoto, Masaru, 2012, The subgenus Pentapedilum Kieffer (Diptera: Chironomidae) in the Yaeyama Islands, the Ryukyus, Japan, Zootaxa 3191, pp. 33-40 : 35

Polypedilum (Pentapedilum) convexum ( Johannsen, 1932)

( Figs. 7–9 )

Pentapedilum convexum Johannsen, 1932: 540

Polypedilum (Pentapedilum) convexum (Johannsen) : Tokunaga (1964: 596); Cranston (1996: 258); Zorina (2006: 415); Oyewo and Saether (2008: 49) .

Material examined. JAPAN: Kanpira-falls, Iriomote Island, Okinawa, 28–29. VII.1978, 10 males, light trap, I. Kanazawa; as previous except 4.IV.1999, 33 males, sweep net M. Yamamoto; as previous except 20.III.2000, 54 males.

Diagnostic characters. The male is distinct in having a very broad anal point, a needle-like projection of the superior volsella, and cell m basal of RM with more than 50 setae.

Remarks. The species shares a very broad anal point and the presence of a sharply pointed or needle-like projection on the superior volsella in the male genitalia with the following species: Polypoedilum (Pentapedilum) anale ( Freeman, 1954) , P. (Pe.) fanjingense Zhang et Wang, 2005 , P. (Pe.) kasumiense ( Sasa, 1979) and P. (Pe.) toyamadeeum (Sasa, 1996) . The anal point is a sagittate keel-like plate and has a wide dorsal lamella. The anal point, when observed from above, shows various appearances according to the degree of the development of the dorsal lamella. In some cases the shape of the anal point observed laterally is a useful character to separate closely related species.

Oyewo and Saether (2008) suggested that the shape of the median furrow or V-shaped ridge of the anal point was one of the most important identification characters between the above-mentioned species. The median furrow or V-shaped ridge of the anal point sensu Oyewo and Saether (2008) is not observable on the dorsal surface of the anal point. The V-shaped ridge is a tangent line appearing as a result of contact betweem the anal point and the ninth tergum. Furthermore, the median furrow situated posterior to the V-shaped ridge is a structure which occurs as a result of contact between the lateral sagittate keel-like plate and the wide dorsal lamella of the anal point. Judging from the structure of the anal point, it is difficult to accept their opinion that the shape of the structure is characteristic among closely related species.

Among the Japanese species, P. (Pe.) convexum , P. (Pe.) kasumiense and P. (Pe.) toyamadeeum superficially resemble each other. Excluding the V-shaped line on the anal point (V-shaped ridge sensu Oyewo & Saether, 2008 ). P. (Pe.) toyamadeeum is characterized by having a lower antennal ratio (0.34–0.41) than other related species. For the moment we cannot judge whether the difference of the antennal ratios between these two species is useful or not as an identification character, nor can we exclude the possibility that above-mentioned three species are conspecific.

The larvae of this species were collected in small rock pools by the riverside near the Kanpira-falls. On that basis, P. (Pe.) convexum would appear to depend on a lentic environment.

Distribution. Indonesia, Caroline Islands, China, Japan (Iriomote Island, Ryukyus), Russian Far East (Urup Island, Kurile), Bhutan, India, Palau Federated of Micronesia.

Figures

FIGURES 7 – 11. Male genitalia of Polypedilum spp. 7 – 9: P. (Pentapedilum) convexum; 10: P. (Pentapedilum) nodosum; 11: P. (Tripodura) tananence; 7, 10, 11: genitalia, dorsal view; 8: anal point, dorsal view; 9: anal point, lateral view.