Rhithrogena parva (Ulmer, 1912)

Ecdyonurus parvus Ulmer, 1912, male and female imagos

Rhithrogena parva Ulmer 1920

nec Rhithrogena parva (?) Ulmer, 1939, nymphs

Rhithrogena parva Kang & Yang, 1994, nymphs and eggs

Material. 22 pinned syntype specimens (20 males and 2 females): Formosa [Taiwan], Taihorin (= Taihorinsho) [currently known as Dalin, Chiayi County], 16 males, 1 female, VIII. 1909; 1 male, IX.1909; 1 female, VIII.1910; 3 males, XI.1910, H. Sauter leg. [ZMH]

Two males from VIII.1909 [one now in MZL] and the female from VIII.1910 have been rehydrated and are currently in ethanol.

2 nymphs, one entirely mounted on microscopic slide: Taiwan, Fuyan, Juisui, Hualien Hsien, 280 m, 02.I.1991, C.K. Kang leg [MZL]

Male imago. Body length: ca 8 mm; forewing length: ca 8.5 mm.

General coloration medium to dark brown, without specific patterns; abdominal sternites lighter than tergites; forelegs dark brown, mid- and hindlegs medium brown, upper face of femora with large elongated dark macula in middle (Fig. 3); coxae of mid- and hindlegs blackish; cerci entirely medium brown.

Wings translucent, longitudinal veins medium brown. Forewings with apex of the costal and subcostal fields tinted in medium brown; pterostigmatic area with 13–15 simple cross veins.

Forelegs as described and illustrated by Ulmer (1912: Fig. 8), tarsal composition 2>3>4>5>1; segment 1 ca 0.20–0.25x length of segment 2. Tarsal claw with enlarged paddle-like ungula and reduced claw-like one (Fig. 31).

Styliger plate straight to slightly concave, with two lateral rounded, asymmetrical processes (Fig. 27); gonopods 4-segmented, terminal segment slightly smaller than penultimate segment. Penis lobes V-shaped, cylindrical; in ventral view, apical sclerite with small tooth near large and elongate gonopore (Fig. 28); titillators stout and composed of 2–3 teeth at apex and with others scattered on its face (Fig. 28); in dorsal or lateral view (Figs 29–30), large and acute spine at apex, not visible in ventral view.

Female imago. Body length: ca 9 mm; forewing length: ca 10.5 mm.

General coloration as in male, coxae medium brown, wing coloration similar.

Hind leg with very short tarsi, about 0.25x length of tibia; tarsal composition 5>2>1>3=4 (Fig. 3).

Subanal plate clearly concave, median incision shallow (Fig. 32).

Nymph. Described already by Kang & Yang (1994), supplementary information is as follows.

Labrum similar to that of Rh. sumatrana, but tuft of thin and short setae in median position much larger (Fig. 11). Mandibles with row of setae below inner incisor short and not reaching middle of distance to mola (Figs 33–34). Presence of ca 10 comb-shape setae on crown of galea-lacinia, median ones bearing 9–10 teeth. Labium similar, inner angle of paraglossae even more pronounced than in Rh. sumatrana .

Bristles on dorsal face of femora similar to those of Rh. sumatrana, Hind tibiae with tibio-pattelar suture shorter.

Gill I with margin entire and smooth (Fig. 13); plica thin and much shorter than in Rh. sumatrana . Gills II–VII with margin entire. Lateral sclerites of first abdominal sternite directed posteriorly (Fig. 23). Posterior margin of abdominal tergites with row of regular pointed teeth; submarginal microdenticles absent (Fig. 25).

Discussion. Rh. parva clearly possesses all the attributes of the genus Rhithrogena . This is evidenced by the genitalia that are described for the first time, above. The male styliger plate possesses two large humps that are more pronounced than those seen in European species, for instance; the presence of a small ventral apical spine and a larger dorsal one, together with robust titillators, are well-known genital structures within the genus. On the contrary, the cylindrical shape of the penis lobes is somewhat unusual, most of the species having a stronger penis base.

The foreleg claw of the male is also intriguing because it resembles the one found in the subgenus Tumungula; in Rh. parva, the paddle-like claw is greatly enlarged, much more than in other species of Rhithrogena s.s. In Rh. (Tumungula) unica, the second claw is described as “small, blunt, plate-shaped”, whereas in Rh. parva it retains the hooked form as in other legs. The tarsal composition of the foreleg, with the first segment greatly reduced, the absence of acute processes on the styliger margin, and the presence of genital titillators are typical of Rhithrogena s.s.

The nymph of Rh. parva is easily told from the one of Rh. sumatrana by the shape of the gill I, the shape of the lateral sclerites of the first abdominal sternite, the number of teeth of the comb-shape structures of the galea lacinia, the setation of the labrum, and also by the ornamentation of the abdominal tergites.