Stonefly Species Skwala compacta (Large Springflies)

Source: A taxonomic revision of the genus Arcynopteryx Klapálek, 1904 (Plecoptera, Perlodidae)

Diagnosis. Abdominal segments 1 - 2 are divided by a pleural fold. The submental gills are long and conical. The arms of the mesosternal ridge meet the anterior corners of the furcal pits, the transverse suture is absent. The stylet of the epiproct as a long, fine bristle is absent. The male of Skwala compacta comb. nov. can be distinguished by the shape of the hemitergal lobes, which are simple, cylindrical, wide, short, flat and slightly curved upward along the posterior margin. The hemitergal lobes are directed towards the middle transversely, and covered by small, stout setae (Figs 40 - 43). The lever arm is short, stout and slightly curved; the epiproct is short, blunt and spoon shaped, with a soft distal part and a finger-shaped top (Fig. 44), the top is densely covered with thin, clear spines. The lateral stylets are attached laterally to the folds of the cowl only the pointed sclerotized tips are clearly pronounced (Fig. 44). The everted aedeagus is large and membranous, with a pair of distinct lateral rounded lobes at the dorsolateral margins; one large lobe rounded dorsally is present between the lateral lobes; one small knob is located apically; two broadly rounded swellings project posterolaterally and slightly below the large lobe; tiny, clear, erect spinules densely cover the aedeagal surface ventrally and laterally; reddish spinules are grouped in a triangle on the dorsal surface of the large lobe basally and continue dorsomedially to the small knob (Fig. 42).

The female has a large subgenital plate, its posterior margin slightly rounded and sclerotized, with two shallow notches medially; the plate is covered with small, darkish setae (Fig. 45).

The egg is spindle-shaped (Fig. 46). The collar is stalked; the sides of the collar bear several sharp longitudinal carinae (Fig. 47). The chorion is covered with closely packed hexagonal FCIs (Figs. 46 - 48); the FCI walls are thin, consisting of shallow furrows; the floors are flat with 4 - 8 small punctations medially (Fig. 48).

Adult habitus. The head is brown, with a yellow spear-shaped spot in the interocellar area, not reaching the median ocellus and continued to the occiput medially, where the spot is slightly enlarged (Fig. 39). A dark brown spot projects onto the clypeus in front of the brownish M-line. The tentorial pits are brown; the lateral margins of the clypeus are pale. The pair of tentorial pits in front of the lateral ocelli and the pair of small oval patches lateral to the lateral ocelli are brown. A posterolateral spot with brown callosities is weakly recognizable behind each compound eye. The antennae and palpi are brown. The pronotum is almost square or slightly longer in width than in length, brown with a yellow medial band and prominent dark brown rugosities (Fig. 39). The medial band expands in the last quarter of the length of the pronotum. The mesonotum and metanotum are dark brown. The anterior margin of the femur is dark brown. The tibia is light brown with a thin dark brown stripe basally. The wings of the male and female are slightly shortened and extend to the top of the abdomen. The RS of the forewing has three or more branches; the apex exhibits a random network of cells formed by the transverse veins and branches of the RS. The cerci are longer than the abdomen, ringed, and covered with long colorless hairs. Each cercal segment is pale basally and blackish distally. The apical cercal segments are completely blackish with the exception of the pale bases (Fig. 39). The submental gills are long and conical. The arms of the mesosternal ridge meet the anterior corners of the furcal pits, a transverse suture is absent.