Cincticostella jianchuan Sun, Yang, Tan, Li & Jacobus, 2024, sp. nov.

Cincticostella jianchuan sp. nov.

Figs 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20

Material examined.

Holotype: male imago, with final nymphal instar exuviae (in ethanol), China, Yunnan Province, Dali City, Jianchuan County, Jinlong River, 26 ° 35 ' 2.7 " N, 99 ° 51 ' 45.0 " E, 2371 m a. s. l., 09. V. 2022, coll. Xian-Fu Li and Rong-Long Yang. Paratypes: 40 nymphs, 24 imagos and 20 subimagos reared from nymphs with same data as holotype.

Diagnosis.

The new species is similar to C. fusca. These two species can be differentiated from other Cincticostella species by the following combination of characters in the nymph: 1) caudal filaments length subequal to or slightly shorter than body length, 2) genae developed into obvious extensions, 3) mesothoracic projection with notch, 4) forefemur without transverse row of setae on upper surface, and 5) all articulations of caudal filaments with spines; and by the following combination of characters in the male imago: 1) area between C, Sc and R 1 of forewings colored, 2) styliger plate with median convex lobe-like posterior projection, and 3) general shape of penes, especially the form of the apical sclerite on the ventral face.

The new species can be distinguished from C. fusca in the male imago stage by its coloration, its mesonotal scutellum morphology, and by the shape of genitalia. In the nymphal stage, the two species can be distinguished by the setation of abdominal terga and the shapes of posterolateral projections of tergum IX. Specifically:

Cells of costal and subcostal fields of the forewing of C. jianchuan sp. nov. are brown (Figs 7 E, 10 D, 17 A, B), whereas these cells are dark brown in C. fusca (Zhang et al. 2020: fig. 4 A, B).

The mesonotum of C. jianchuan sp. nov. clearly has three projections on the posterior margin (Fig. 8 A), while C. fusca has only two projections apparent (Zhang et al. 2020: fig. 4 D).

Cincticostella jianchuan sp. nov. has two subapical hemispherical grooves on the ventral face of the penes (Fig. 9 B, E), but C. fusca has two additional large ventral projections on the upper middle of the ventral face of the penes (Zhang et al. 2020: fig. 5 C, E).

In terms of wing venation, the stem of the MA + Rs fork of C. jianchuan sp. nov. occurs at a slightly more distal location than the fork of MP (Fig. 7 E). However, in C. fusca, the MP fork and the stem of the MA + Rs fork are equidistant from the base of the wings to the margin (Zhang et al. 2020: fig. 6 A).

The posterolateral projections of abdominal segment IX of the nymph of C. jianchuan sp. nov. (Fig. 5 A, C, D) are longer than the same posterolateral projections on C. fusca (Kang and Yang 1995: fig. 3 H).

Also on the nymph, each lateral margin of abdominal segments IV – VIII and median area of terga II – X of C. fusca nymph has setae (Kang and Yang 1995: fig. 3 G). In contrast, the nymph of C. jianchuan sp. nov. lacks setae in the corresponding locations (Fig. 5 A, B).

Descriptions.

Last instar nymph (in alcohol). Last instar nymph: head width, male 3.1–3.3 mm; female 3.4–3.5 mm; body length (excluding tails), male 15.3–16.7 mm, female 18.0– 18.9 mm; cerci length, male 8.9–11.6 mm, female 10.5–12.8 mm, middle caudal filament, male 9.3–10.9 mm, female 10.6–11.5 mm. Body color reed green to brown (Fig. 1 A – C).

Head: base color reed green to brown, genae expanded into lobes (Fig. 2 A); middle portion of antennae with tiny setae on articulations (Fig. 2 C), basal (Fig. 2 B) and apical (Fig. 2 D) portions of antennae without such setae. Labrum width equal to about 1 / 3 head width, setae on dorsal and ventral surfaces; those on ventral surface and anterolateral margin relatively longer and more densely arranged (Fig. 2 E). Mandible: both mandibles with numerous short hair-like setae on dorsal and lateral surfaces; trifurcated outer incisor and bifurcated inner incisor (Fig. 2 F, G). Left mandible without seta near mola, prostheca comprised of two tufts of spines with common stem (Fig. 2 F). Right mandible with row of irregular hair-like setae under mola, prostheca with one tuft of hair-like setae on common base (Fig. 2 G). Hypopharynx (Fig. 2 H): lingua recumbent oval, with shallow anteromedian concavity, short setae densely situated on anterolateral margins, apical 1 / 4 with pale spot; superlinguae with slight curved outer, anterior margin and surface densely covered with long setae. Maxilla (Fig. 2 I – K): apex with 2 large canine teeth and slightly curved plate, apical margin of plate crenate (Fig. 2 K); tuft of stout setae at apex; galea-lacinia with several setae near base; lateral margins of stipes and cardo with fine setae; three-segmented maxillary palp covered with hair-like setae and sharp setae, segment III very small and short, segment length ratio from base to apex = 5.3: 4.7: 1.0 (Fig. 2 I – K). Labium (Fig. 2 L): paraglossae semicircular, apical half of dorsum with closely set sharp setae; apical three quarters of venter with loose set of fine setae; glossae long and ellipsoid with setae; labial palp with 3 segments, surfaces of segments I and II with sharp setae; segment II slightly enlarged; segment III very small, segment length ratio from base to apex = 7.2: 5.1: 1.0.

Thorax general color yellowish to reed green. Pronotum with paired small brownish green irregular stripes, anterolateral corners produced anteriorly (Fig. 1 A, B); mesonotum with medial pale stripe, paired small brownish green dots and irregular stripes (Fig. 1 A, B), lateral margins each with blunt projection near anterolateral corner (Figs 1 A, B, 3 A). Prosternum with pair of hole-like structures (Fig. 3 B, indicated by black arrow). Legs: posterolateral angles of fore and middle coxae each with acute projection (Fig. 1 A). Dorsal surface of femur of each leg with setae on median, posterior and anterior areas (Fig. 4 A – C), ratio of overall femur width of foreleg: middle-leg: hindleg = 1.0: 1.0: 1.1. Ratio of femur: tibia: tarsus of foreleg = 1.9: 1.8: 1.0, ratio of femur: tibia: tarsus of middle-leg = 2.4: 2.4: 1.0, ratio of femur: tibia: tarsus of hindleg = 2.6: 3.0: 1.0. Claws pale, apices dark brown, with 4–5 blunt denticles medially (Fig. 4 D, E).

Abdomen: abdominal segments II – IX each with posterolateral projection with clavate setae; largest posterolateral projection on segment VIII, long and divergent posterolateral projections on segment IX (Fig. 5 A). Posterior margins of segments II – IX each with pair of sharp tubercles, progressively longer on segments II – VIII (Fig. 5 A). Each tergum without setae on posterior margin and dorsal area (Fig. 5 A, B), but posterior margin of tergum I with long fine setae. Posterior margin of sternum IX of male wavy (Fig. 5 C); posterior margin of sternum IX of female concave (Fig. 5 D). Gills III – V subequal in size, dorsal lamellae oblique oval, ventral lamellae each with deep cleft (Fig. 6 A – C); gill VI dorsal lamella rounded, ventral lamella without deep cleft (Fig. 6 D); gill VII small, somewhat heart-shaped but rounded (Fig. 6 E). Distal part of caudal filaments darkly colored, each segment with whorled acute setae at apex and few sharp setae near middle area, median segments with long fine setae on lateral margins loosely arranged (Fig. 6 F).

Male imago (in ethanol). Body length 18.3–18.8 mm (excluding tails), head width 3.1–3.3 mm, forewing length 19.4–20.0 mm, hindwing length 5.4–5.9 mm, cerci length 8.9–11.6 mm, middle caudal filament 9.3–10.9 mm. Body color brown to dark brown (Figs 7 A – C, 17 A).

Head. Compound eyes contiguous, upper portion brown and lower portion black (Fig. 7 B, D).

Thorax. Pronotum with expanded posterolateral air sac-like structure (Fig. 7 A – D, indicated by red arrow). Mesonotum with three projections on posterior margin, middle projection short (Fig. 8 A, indicated by red arrow). Forewings generally hyaline, veins brown; all cells of costal and subcostal fields tinted with brown, 2 / 3 cells from base to margin of subcostal and radial fields tinted with brown; cross veins in stigmatic area slightly oblique, and those between costal and subcostal areas separated into two rows of cells. MA forked 2 / 3 of distance from base to margin; stem of MA + Rs fork at very base, just slightly more distal than fork of MP (Fig. 7 E). Hindwing totally hyaline, leading margin slightly concave; MA single, MP forked symmetrically (Fig. 7 F). Forelegs brown to dark brown (Fig. 8 B), mid- and hindlegs brown (Fig. 8 C, D). Femur: tibia: tarsus of foreleg = 1.0: 1.3: 1.6, tarsal segments from basal to apical = 1.0: 5.4: 5.0: 3.5: 1.8; femur: tibia: tarsus of midleg = 2.2: 2.3: 1.0, tarsal segments arranged in decreasing order = 1.0: 1.4: 1.3: 1.0: 2.5; femur: tibia: tarsus of hindleg = 2.6: 3.0: 1.0, tarsal segments arranged in decreasing order = 1.0: 1.3: 1.5: 1.1: 2.9. Claws of all legs similar, one blunt and one hooked.

Abdomen. Terga II – V each with pale stripe on posterior margin, pair of diffuse dark dots near posterior margins of terga II – IX; diffuse dark stripes on middle and lateral faces of terga VIII – IX (Fig. 7 A, B). Dark ganglionic marks on sterna I – VII (Fig. 7 C). Small portion of sternum VII and most of sterna VIII – IX light colored (Fig. 7 C). Styliger plate with middle projection (Fig. 7 C). Caudal filaments brown to dark brown, with spines (Fig. 8 E, F).

Genitalia. Forceps covered with stout setae; segment 3 globular; segment 2 angled inward distally and with slight subapical constriction (Fig. 9 A – C). Penis lobes compact, with linear groove on apical 1 / 2 of dorsal face (Fig. 9 A, D), apical sclerite (Fig. 9 C, F), two subapical hemispherical grooves (Fig. 9 B, E, indicated by red arrows), one basal obvious bump (Fig. 9 B, E), one subapical large pale plate on ventral face (Fig. 9 C, F), lobes separated by slight cleft (Fig. 9 C, F).

Female imago (in ethanol). Color pattern similar to male (Figs 10 A – F, 11 A – C, 17 B); body length 19.1–22.9 mm (excluding tails), head width 2.9–3.5 mm, cerci length 17.6–23.7 mm, middle caudal filament 17.3–22.1 mm, forewing 19.9–23.4 mm, hindwing 5.5–6.1 mm. Lengths of femur: tibia: tarsus of foreleg = 1.9: 1.6: 1.0, tarsal segments from basal to apical = 1.0: 2.0: 1.7: 1.1: 2.3; femur: tibia: tarsus of midleg = 2.4: 2.4: 1.0, tarsal segments from basal to apical = 1.0: 1.2: 1.2: 1.1: 3.2; femur: tibia: tarsus of hindleg = 2.7: 3.1: 1.0, tarsal segments from basal to apical = 1.0: 1.1: 1.4: 1.0: 2.7. Compared with male, pronotum with nonexpanded posterolateral air sac-like structures; inner margin of femur of foreleg covered with spines. Posterior margin of subgenital plate produced to 1 / 5 length of sternum VIII. Posterior margin of subanal plate with obvious median cleft (Fig. 10 F). Color pattern of caudal filaments similar to male.

Male subimago. Body color taupe gray to dark brown (Figs 12 A – C, 17 B). Front portions of forewing and hindwing taupe gray and rear portions nearly white (Fig. 13 A, B). Pronotum with nonexpanded posterolateral air sac-like structures; scutellum with three long, pointed posterior prolongations (Fig. 12 A, B). Caudal filaments with relative densely spines (Fig. 14 E). Apical sclerite of penes incomplete (Fig. 13 C). Body length 13.0– 14.5 mm (excluding tails), head width 2.6–3.0 mm, cerci length 8.0– 16.5 mm, middle caudal filament 8.5–16.4 mm, forewing 19.4–19.8 mm, hindwing 4.6–5.1 mm (Fig. 12 A – C, 13 A – C, 14 A – E). Margins of femur and tibia of foreleg, midleg and hindleg all densely covered with spines (Fig. 14 A – D). Length of femur: tibia: tarsus of foreleg = 1.3: 1.4: 1.0, tarsal segments from basal to apical = 1.0: 2.7: 2.5: 1.8: 2.2; femur: tibia: tarsus of midleg = 2.4: 2.3: 1.0, tarsal segments from basal to apical = 1.2: 1.7: 1.3: 1.0: 2.9; femur: tibia: tarsus of hindleg = 3.1: 3.6: 1.0, tarsal segments from basal to apical = 1.0: 3.0: 3.0: 2.0: 6.2.

Female subimago (in alcohol). Similar to male subimago except for usual sexual differences (Figs 15 A – C, 16 A – E, 17 C). Length of femur: tibia: tarsus of foreleg = 1.7: 1.6: 1.0, tarsal segments from basal to apical = 1.0: 1.7: 1.4: 1.0: 2.1; femur: tibia: tarsus of midleg = 2.4: 2.5: 1.0, tarsal segments from basal to apical = 1.0: 1.3: 1.3: 1.2: 2.8; femur: tibia: tarsus of hindleg = 3.1: 3.6: 1.0, tarsal segments from basal to apical = 1.0: 1.7: 1.4: 1.3: 3.2. Inner margins of tarsus of foreleg, midleg and hindleg densely covered with spines (Fig. 8 D – F, J). Head width 2.9–3.6 mm, body length 17.5–19.7 mm (excluding tails), forewing length 18.6–22.2 mm, hindwing length 3.8–5.7 mm, cerci length 12.2–13.8 mm, middle caudal filament 13.0– 13.8 mm.

Eggs: dissected from female imago. Length 142–207 μm, width 96–120 μm. Ovoid with polar cap composed of dense filaments, each filament with intumescent terminal (Fig. 18 A, B). Chorion with irregular polygonal ridges except subpolar areas (Fig. 18 A – D); mesh with variety of tubercles medially; knobs of attachment structure and micropyle distributed near equator (Fig. 18 A, C).

Persistent mouthparts of winged stages.

The new species presents persistent but vestigial mouthparts in the winged stages; in ventral view of head, the labium is present and clearly visible (Fig. 19 A – D, indicated by red arrow).

Etymology.

The specific epithet is named after the type locality, Jianchuan County, Dali Bai Autonomous Prefecture, Yunnan Province, China. The English common name of this species is the Jianchuan spiny crawler mayfly. The Chinese name is 剑川带肋蜉.

Distribution.

Yunnan, China.

Ecology.

The nymphs of this new species were collected from upstream reaches of the Jinlong River in Jinchuan County, Dali Bai Autonomous Prefecture, Yunnan Province. The nymphs prefer run and riffle habitats containing stones of various sizes (Fig. 20 A, B). Sampling sites were located at high altitudes (above 2300 m); the river and associated riparian zone passed through relatively natural habitat or traditional agriculture; width of the river was 3.0– 9.7 m, but can reach 15 m during the flood season (Fig. 20 A); the water quality tended to be alkaline (pH = 9.04). In the laboratory, the mature nymphs quickly completed the molting process on the water surface from 9 pm to 12 pm at night. The subimago stage persisted until the third noon or afternoon, with the observed lifespan of imagoes being about 3–4 days.