Styloperla inae Chao, 1947

Chen, Zhi-Teng, 2023, The little-known larval morphology of two stoneflies of Styloperlidae (Insecta: Plecoptera) in China, Zootaxa 5244 (4), pp. 361-376 : 362-365

Styloperla inae Chao, 1947

Figs. 1–9

Material examined. China: Zhejiang: Mt. Yaowang ( Fig. 1A ), 28°52′42.63′′N, 118°55′22.45′E, 250 m, 7 male adults ( Fig. 1B ), 2 female adults, 3 male larvae, 28. iv. 2020, leg. Xiao-Han Ye (ICJUST).

Description of mature male larvae. Body slender ( Fig. 2A, B ), length ca. 12 mm (excluding antennae and cerci), generally pale brown, without gills.

Head. Biocellate. Background pigmentation pale brown, covered by sparse fine hairs, with a longitudinal dark spot of the adult showing through nymphal skin ( Fig. 3A–C ). Clypeus with dense short setae on posterior half. Ecdysial suture distinct. Compound eyes small, dark, and glabrous; each eye with a pair of long setae along inner margin. Occiput covered with dense, prostrate setae on posterolateral areas. Antennae slender ( Fig. 3D ), subequal in length to the abdomen, brown basally, discolored toward apex; scapus with an apical fringe of dense, stout setae interrupted dorsally and ventrally; other segments apically fringed with sparse, short setae.

Mouthparts. Labrum with a transverse patch of dense long setae on medial area and two anterolateral patches of moderate setae ( Fig. 4A ). Submentum rounded, covered by dense long setae ( Fig. 4B ). Apical segment of labial palp subequal in length to the penultimate one, apex covered with stout setae ( Fig. 4B ). Paraglossae slightly larger than glossae which are separated from each other by a median sclerite ( Fig. 4B ). Cardo of maxilla slender, dorsally and laterally with a few long setae ( Fig. 5A–D ). Stipes broad, covered with long setae on both dorsal and ventral surfaces. Galea finger-shaped, outer margin fringed with curved hairs on apical half and flattened moderate setae throughout, inner margin with a comb of erected setae in the middle, apex with a bunch of stout setae. Lacinia subequal in length to galea, with three apical teeth, inner margin with a row of long setae extending dorsad, dorsal surface with a subapical row of moderate setae near the marginal setae. Maxillary palp segments III–V equal in length, apex with stout setae. Right mandible with two apical teeth whose line is prolonged posteriorly to the end of inner margin ( Fig. 6A, B ). Left mandible with five apical teeth whose line is prolonged posteriorly into the ventral humps on the mola ( Fig. 6C, D ). Left mola with a blade-like inner edge on dorsal surface; right mola with inner marginal concave areas on dorsal surface. Both molae with short hairs on posterointernal angle of ventral surface, and a row of long hairs on posterointernal margin which connected with a dorsal patch of short hairs.

Thorax. Pronotum subquadrate, near as wide as head, length half the width, outline dark, corners obtuse and each with about two long setae ( Fig. 3A–C ); background pigmentation pale, median suture and its two lateral longitudinal bands dark brown, surface covered with hairs. Meso- and metanota background pigmentation pale, most areas covered with dense, dark setae. Wing pads of equal size, pale brown, covered with setae similar to those on meso- and metanota, lateral and posterior margins fringed with additional short spines, ventral surface with dense long spines on basal two-thirds, inner margins concave in forewing pads and straight in hind wing pads ( Fig. 3A, B ). Thoracic sterna covered with brown hairs ( Fig. 3C ); each sternum with a dark brown stigma covering furasternal pits, Y-arms and mesosternal Y-stem. Spinasternum of prothorax separated from furcasternum.

Legs. Coxae and trochanters covered with dark setae and fringed with stout spines mainly on dorsal surfaces ( Figs. 3A–C and 7A–F ). Femora dorsally and ventrally covered with dense dark setae except for a longitudinal glabrous stripe near outer margin, anterior margin fringed with several short dark spines, posterior margin with dense long spines and swimming hairs mainly on distal half. Tibiae covered with dense dark setae on both dorsal and ventral surfaces, inner and outer margins fringed with dense long spines, outer margin with dense long swimming hairs, distal margin fringed with stout trifurcate setae but without spurs ( Fig. 7A–G ). Tarsal segments covered with dense setae and with long swimming hairs along outer margin; the first two tarsal segments shortest, apical tarsal segment of foreleg and midleg with bud-like setae. Claws sharp and glabrous.

Abdomen. Abdominal sternum I fused with metasternum, segment II divided into terga and sterna by membranous pleura ( Fig. 8A, B ); each segment covered with dense dark brown setae on both dorsal and ventral aspects, and fringed with dense moderate setae and several longer setae along posterior margin. Tergum X with rounded posterior margin. Paraprocts slender and conical, apex membranous and with dense stout setae. Cerci brown to pale brown ( Fig. 9A, B ), shorter than abdomen, with both dorsal and ventral fringe of long swimming hairs; each segment with apical fringe of both stout and long setae, length of the longest setae exceeds the segment length.

Distribution. The species was originally described from Fujian Province of southeastern China ( Chao, 1947). This study slightly extends its distribution records northward into Zhejiang Province.

Figures

FIGURE 1. Styloperla inae Chao, 1947. (A) Habitat in Mt. Yaowang, Zhejiang, China. (B) Habitus of male adult.

FIGURE 2. Styloperla inae Chao, 1947, male larva. (A) Habitus, dorsal view. (B) Habitus, ventral view. Scale bars: 1.0 mm.

FIGURE 3. Styloperla inae Chao, 1947, male larva. (A) Head and thorax, dorsal view. (B) Head and thorax, lateral view. (C) Head and thorax, ventral view. (D) Basal and apical segments of antenna, lateral view. Scale bars: 1.0 mm for (A–C), 0.1 mm for (D).

FIGURE 4. Styloperla inae Chao, 1947, male larva. (A) Labrum, dorsal view. (B) Submentum, ventral view. Scale bars, 0.1 mm.

FIGURE 5. Styloperla inae Chao, 1947, male larva. (A) Right maxilla, ventral view. (B) Left maxilla, dorsal view. (C) Left maxilla, dorsal view. (D) Right maxilla, dorsal view. Scale bars, 0.1 mm.

FIGURE 6. Styloperla inae Chao, 1947, male larva. (A) Right mandible, ventral view. (B) Right mandible, dorsal view. (C) Left mandible, dorsal view. (D) Left mandible, ventral view. Scale bars, 0.1 mm.

FIGURE 7. Styloperla inae Chao, 1947, male larva. (A) Right foreleg, ventral view. (B) Right foreleg, dorsal view. (C) Right midleg, ventral view. (D) Right midleg, dorsal view. (E) Right hind leg, ventral view. (F) Right hind leg, dorsal view. (G) Details on apex of right hind leg, dorsal view. Scale bars, 0.5 mm.

FIGURE 8. Styloperla inae Chao, 1947, male larva. (A) Abdomen, dorsal view. (B) Abdomen, ventral view. Scale bars, 1.0 mm.

FIGURE 9. Styloperla inae Chao, 1947, male larva. (A) Basal segments of cercus, lateral view. (B) Apical segments of cercus, lateral view. Scale bars, 0.1 mm.