Skwala compacta (McLachlan 1872)

Chen, Zhi-Teng, 2022, Comparative larval morphology of two stoneflies of Perlodidae (Insecta: Plecoptera), Zoologischer Anzeiger 299, pp. 115-127 : 119-123

3.2. Skwala compacta (McLachlan 1872)

3.2.1. Material examined.

10 males, 4 females, 1 larva, Irtysh River , Fuyun County, Xinjiang Uygur Autonomous Region, China, 46.9858 ◦ N, 89.5230 ◦ E, 800 m, 19.04.2019, Zhi-Teng Chen ; 43 males, 13 females, 20 larvae, 18 exuviae,

Shudugang River ( Fig. 10 ), Diqing Tibetan Autonomous Prefecture, Yunnan Province, China, 27.7994 ◦ N, 99.8961 ◦ E, 3404 m, March 30 to April 1, 2021, Zhi-Teng Chen; 21 males, 3 females, 4 larvae, 12 exuviae, north of Benzilan Town , Diqing Tibetan Autonomous Prefecture, Yunnan Province, China, 28.2296 ◦ N, 99.2720 ◦ E, 2387 m, 04.04.2021, Zhi-Teng Chen ; 50 males, 8 females, 22 larvae, 19 exuviae, Liupan Mountain , Guyuan City, Ningxia Hui Autonomous Region, China, 35.3641 ◦ N, 106.3115 ◦ E, 2000 m, 11.04.2021, Si-Kai Du .

3.2.2. Description of male larvae

Body length 15–20 mm ( Fig. 11A ). Head background pigmentation pale ( Fig. 11B ). Frons mostly dark brown, with a pale M-line. Posterior area of M-line dark brown, with two pairs of pale spots lateral to the three ocelli ( Fig. 11B ). Ecdysial suture distinct. Occiput covered with dense, dark, short setae on anterolateral areas which medially interrupted by the median epicranial suture, posterolateral areas with sparse, shorter dark setae, laterally with two oval areas which have fewer irregular rows of setae; the transverse occipital row of spines extending from below eye to near median epicranial suture, irregular and sinuous on dorsal aspect ( Fig. 11B ). Compound eyes small, dark and glabrous; postocular fringe distinct ( Fig. 11B ). Submentum of labium rounded, with a concave anterior margin, lateral margins fringed with moderate dark spines ( Fig. 11C ); submental gills finger-shaped ( Fig. 11C ); glossae of labium much shorter than paraglossae ( Fig. 11C ). Antennae pale brown and slender ( Fig. 11D ), subequal in length to the abdomen, each segment apically fringed with dense short setae, basal segments covered with additional dense dark setae.

Cardo of maxilla ventrally covered with sparse patch of flattened, dark setae except for a glabrous rounded area ( Fig. 12A and B ), laterally with ca. 15 stout spines. Stipes elongated, both dorsally and ventrally with flattened setae similar to those of cardo, mainly on outer margins ( Fig. 12A–D ). Galea finger-shaped, posterior half of inner margin with ca. 7 sparsely located thin setae, apically with ca. 3 moderate spines ( Fig. 12A–D ). Lacinia bidentate, much longer than galea, submarginal row with ca. 4 medially interrupted slender setae beginning at base of apical tooth, ending at the inner margin of subapical tooth; dorsal seta located below inner margin of subapical tooth; ca. 15 marginal setae widely spaced and initially long-stout, posterior ones mixed with thinner marginal setae and blending into dorsal surface setae; ventral surface setae scattered below submarginal and marginal setae; several thin, curved dorsal surface setae located near posterior end of the inner lacinia margin. Maxillary palp near glabrous except for several occasionally present short spines on segments1–3 ( Fig. 12A–D ). Mandible with five pointed apical teeth ( Fig. 13A–D ), the four longest teeth each with serrated inner margin; a huge hairbrush present posterior to the apical teeth ( Fig. 13A–D ); both ventral and dorsal surfaces of mandible with spine patches near the hairbrush ( Fig. 13A–D ); outer margin ventrally with flattened setae ( Fig. 13A and B ) and dorsally with both setae and moderate spines ( Fig. 13C and D ).

Pronotum subquadrate ( Fig. 14A ), much narrower than head, corners obtuse; background pigmentation pale, mostly covered with dark setae except the irregularly shaped glabrous areas which have obscure borders, median line without long hairs; margins fringed with densely located, moderate to long spines ( Fig. 14A ). Meso- and metanota background pigmentation pale, with both dark setae and irregular glabrous areas ( Fig. 14A ). Wing pads short, indicating brachypterous male adults, pale ( Fig. 14A ), covered with sparse dark setae, outer margins near straight and fringed with short spines, inner margins concave in forewing pads and rounded in hind wing pads. Anterior and posterior areas of each thoracic sternum covered with dark setae ( Fig. 14B ). Apex of mesosternal Y-stem connected to anterior corners of furcal pits ( Fig. 14B ). Coxae and trochanters covered with dark setae and fringed with short spines mainly on dorsal surfaces ( Fig. 15A–C ). Femora dorsally covered with dense dark setae except for a longitudinal glabrous stripe near outer margin ( Fig. 15A–C ), ventrally near glabrous except the anterior margins ( Fig. 15D–F ), posterior margins with dense, long swimming hairs. Tibiae dorsally covered with dense dark setae on anterior half ( Fig. 15A–C ), anterior margin fringed with sparse, short spines, ventrally with a longitudinal row of short spines ( Fig. 15D–F ), posterior margins with dense, long swimming hairs. Two stout tibial spurs present. Tarsal segments with short spines along inner margin, surface covered with sparse short setae ( Fig. 15A–F ). Claws sharp and glabrous.

Abdominal segments divided into terga and sterna at the first two segments by membranous pleura, covered with dense dark setae mainly on dorsal aspects except for anteromedial area of each tergum ( Fig. 16A and B ), each segment fringed with conical spines along posterior margin; terga 1–9 each with a transverse row of small pale pits ( Fig. 16A ). Abdominal tergum 10 with a pale median area and covered with several short spines, posterior margin truncate and slightly notched ( Fig. 16A ). A conical process present posterior to tergum 10, which with an anchorshaped scletite and a pointed apex ( Fig. 16A ). Paraproct sclerites triangular and covered with long spines, apices pointed ( Fig. 16B ). Cerci pale, subequal in length to the abdomen, swimming hairs short and sparse, each segment apically fringed with slender spines, length of which does not exceed the segment length ( Fig. 16C ).

3.2.3. Description of female larvae

Body length 20–25 mm. Color pattern, chaetotaxy, and structure of head ( Fig. 17A and B ), thorax ( Fig. 18A and B ), abdomen ( Fig. 19A and B ), and appendages almost identical to those of the male larvae. Abdominal tergum 10 with a smaller pale median area and covered with short spines on posterior half of the tergum, posterior margin subtriangular ( Fig. 19A ). Posterior margin of sternum 8 produced into a trapezoidal sclerite ( Fig. 19B ). Paraproct sclerites long triangular and covered with dense, long conical spines ( Fig. 19B ).

3.2.4. Distribution

The species is widespread in the eastern Palaearctic Region and previously known from Japan, Mongolia, Russia, and Xinjiang Uygur Autonomous Region of northwestern China (Chen 2019 b). This study greatly extends its distribution in China eastwards to Ningxia Hui Autonomous Region and southwards to Yunnan Province.

3.2.5. DNA barcodes

To promote the molecular identification of the widespread S. compacta, the DNA barcodes, i.e., the COI sequences are obtained for the specimens from Yunnan and Ningxia (ON644610– ON 644611), respectively. A high intraspecific sequence divergence (9 %) is found between the specimens from Yunnan and Ningxia, which is unsurprising for a widespread stonefly species as already found in the DNA barcoding work of Chen et al. (2020). The two sequences of S. compacta included in this study were generated from an ongoing project of barcoding Chinese stoneflies and more molecular data will be accumulated outside of this study.

Figures

Fig. 10. Skwala compacta (McLachlan 1872) (A) Habitat in Shudugang River, Yunnan Province, China (B) Habitus of living female adult.

Fig. 11. Skwala compacta (McLachlan 1872), male larva from Yunnan (A) Habitus, dorsal view (B) Head and pronotum, dorsal view (C) Head and pronotum, ventral view (D) Antenna, lateral view. Scale bars: 1 mm.

Fig. 12. Skwala compacta (McLachlan 1872), male larva from Yunnan (A) Right maxilla, ventral view (B) Left maxilla, ventral view (C) Left maxilla, dorsal view (D) Right maxilla, dorsal view. Scale bars: 0.5 mm.

Fig. 13. Skwala compacta (McLachlan 1872), male larva from Yunnan (A) Right mandible, ventral view (B) Left mandible, ventral view (C) Left mandible, dorsal view (D) Right mandible, dorsal view. Scale bars: 0.25 mm.

Fig. 14. Skwala compacta (McLachlan 1872), male larva from Yunnan (A) Thorax, dorsal view (B) Thorax, ventral view. Scale bars: 1 mm.

Fig. 15. Skwala compacta (McLachlan 1872), male larva from Yunnan (A) Right foreleg, dorsal view (B) Right midleg, dorsal view (C) Right hind leg, dorsal view (D) Right foreleg, ventral view (E) Right midleg, ventral view (F) Right hind leg, ventral view. Scale bars: 1 mm.

Fig. 16. Skwala compacta (McLachlan 1872), male larva from Yunnan (A) Abdomen, dorsal view (B) Abdomen, ventral view (C) Cercus, lateral view. Scale bars: 1 mm.

Fig. 17. Skwala compacta (McLachlan 1872), female larva from Yunnan (A) Head and pronotum, dorsal view (C) Head and pronotum, ventral view. Scale bars: 1 mm.

Fig. 18. Skwala compacta (McLachlan 1872), female larva from Yunnan (A) Thorax, dorsal view (B) Thorax, ventral view. Scale bars: 1 mm.

Fig. 19. Skwala compacta (McLachlan 1872), female larva from Yunnan (A) Abdomen, dorsal view (B) Abdomen, ventral view. Scale bars: 1 mm. Declaration of competing interest