Isca acutata, Gong & Zhou, 2025

Isca acutata sp. nov.

Figs 1 View Figure 1 , 2 View Figure 2 , 3 View Figure 3 , 4 View Figure 4 , 5 View Figure 5 , 6 A View Figure 6

Material examined.

Holotype • 1 male imago, Shuiman Village , Wuzhishan City, Hainan Province, China, 730 m a. s. l., 18.907855°N, 109.679361°E, 2024-I-8-10, Dewen Gong, Xuhongyi Zheng leg. GoogleMaps Paratypes • 1 male imago (reared from nymph) and 10 nymphs, same data as holotype GoogleMaps .

Other material.

• 3 female subimagoes (reared from nymphs), 21 nymphs, Limu Mountain , Wuzhishan City, Hainan Province, China, 627 m a. s. l., 19.169685°N, 109.746047°E, 2023-IV-29, Dewen GONG, Xiaofang Chen, Xinhe Qiang leg. GoogleMaps • 4 nymphs, Jianfengling Moutain , Ledong County, Hainan Province, China, 850 m a. s. l., 18.743911°N, 108.854413°E, 2022-VI-29, Dewen Gong, Manqing Ding, Xinhe QIANG leg GoogleMaps . • 1 nymph, Nandao Farm , Sanya City, Hainan Province, China, 231 m a. s. l., 18.394447°N, 109.388103°E, 2022-VII-6, Dewen Gong, Manqing Ding, Xinhe Qiang leg. GoogleMaps • 2 male imagoes, 5 nymphs, Qixianling Mountain , Baoting County, Hainan Province, China, 280 m a. s. l., 18.702331°N, 109.692115°E, 2024-I-11, Dewen Gong, Xuhongyi Zheng leg. GoogleMaps

Description.

Nymph (in alcohol): Body length 4.2–4.4 mm, cerci subequal to body length, terminal filament 6.4–7.2 mm (Fig. 1 A – C View Figure 1 ). General coloration brown, head and thorax washed light brown, abdominal terga I – VIII brown, terga IX – X light brownish, without any specific pattern, sterna much lighter than terga. Wingpad dark brown, legs uniformly yellowish to amber (Fig. 1 A – C View Figure 1 ).

Head: prognathous, area between three ocelli darker than others (Fig. 1 A, C View Figure 1 ).

Labrum: ca. 1.8 times wider than long, anterior margin concave in the middle, forming a wide V-shape, lateral-anterior angle rounded, lateral-posterior margin shrunken inward; dorsal surface with two rows of setae sub-marginally, setae in the anterior row slender, denser and longer than those in the posterior row, ventral surface with scattered setae near anterolateral angles and a tuft of hair-like setae sub-medially (Fig. 2 A View Figure 2 ).

Mandible: outer margin smoothly convex, with ca. 16 setae at median surface; outer and inner incisors of left mandible divided into three teeth respectively, prostheca with a spur and a tuft of spines; outer incisor of right mandible with 3 teeth (2 tiny denticles on inner tooth), inner incisor with 2 teeth, each of them with additional two acute denticles on both sides; prostheca with a tuft of spines, one bigger than others; four long mesal setae under the molar (Fig. 2 B View Figure 2 ). Hypopharynx: superlinguae with concave lateral margins, two apices extended into oval lobes; apical margin with hair-like setae; two arms of lingua subequal to median oval lobe (Fig. 2 C View Figure 2 ). Maxilla: crown covered with dense of setae, galea-lacinia with row of setae, inner apex with a comb-like setae; maxillary palp three-segmented, length ratio of them from I to III = 1.6: 1.0: 1.0, outer margin of segment I with six setae, segment II with a seta, segment III with two setae, tip of segment III with tuft of relatively short setae; outer margin of stipes with very sparse hair-like setae, outer margin of cardo with six long setae (Fig. 2 D View Figure 2 ). Labium: length ratio of 3 segments of labial palp from I to III = 1.4: 1.1: 1.0; two apical segments slimmer than basal one (Fig. 2 E View Figure 2 ).

Thorax: Setae on outer margin of femur strong, relatively longer than that on inner margin; inner margin of tibiae and tarsi with stout setae; outer margin of tibiae and tarsi with hair-like setae, those on tibia of hindleg with extra stout setae (Fig. 1 D – F View Figure 1 ). Length ratio of femora: tibiae: tarsi of forelegs = 2.3: 1.8: 1.0, that of midlegs = 2.4: 2.0: 1.0, and hindlegs = 2.5: 2.3: 1.0 (Fig. 1 D – F View Figure 1 ). Claw with 14 denticles, distal one larger than others, proximal four denticles smaller (Fig. 1 G View Figure 1 ).

Abdomen: posterior margin of each tergite with contiguous acute spines, posterolateral projections on segment IX only (Fig. 1 A – C View Figure 1 ). Gills present on segments II to VII of ventral side of abdomen (Fig. 1 B View Figure 1 ). Gills similar morphologically, consist of two slender and unbranched lamellae, gills progressively smaller from anterior to posterior (Fig. 1 H – I View Figure 1 ). Caudal filaments brown, terminal filament slightly darker than cerci; posterior margin of each segment with spines, every second segment from segment II with an encircling row of hair-like setae around posteriorly (Fig. 1 A – C View Figure 1 ).

Male imago (in alcohol): Body length 4.4 mm, generally amber to brownish, wings deep brown (Fig. 3 View Figure 3 ).

Head: Width between two compound eyes about half of one eye width; upper half of it orange, lower half black (Fig. 4 A View Figure 4 ).

Thorax: Legs: Foretarsus and tip of tibia pale, other portion brown, ratio of femur: tibia: tarsus = 1.0: 3.8: 3.5, ratio of foretarsal segments from I to V = 1.0: 14.0: 11.9: 8.6: 2.5. Midleg and hindleg dark brown, ratios of femur: tibia: tarsus = 2.9: 2.4: 1.0 and 2.9: 2.5: 1.0 (Fig. 4 B – D View Figure 4 ). Claw dissimilar, one hooked, one blunt (Fig. 4 E View Figure 4 ).

Wing opaque, brown; veins clear, posterior margin with cilia, vein MA forked slightly less than 1 / 2 of distance from base to margin (Fig. 4 F View Figure 4 ).

Abdomen: color of terga I to IX alike, anterior 1 / 3 pale and semi-transparent, posterior 2 / 3 brown, sterna lighter than terga; tergite X brown (Fig. 3 View Figure 3 ). Genitalia: forceps pale; segment I with a mesal expansion at 2 / 5 point; segments II and III subequal, nearly sphere; penes brown, two penes situated together, forming a pen-point like structure, margin of basal half straight, apical half straightly oblique; length of penes about 2 / 5 × of forceps (Fig. 4 G View Figure 4 ). Caudal filaments pale (Figs 3 A View Figure 3 , 4 G View Figure 4 ).

Female: body length 4.1 mm, caudal filaments brown with spine-like setae. Coloration similar to male, sternum IX slightly concave apically (Fig. 5 View Figure 5 ).

Egg.

Egg oval, length about 85 μm, width about 45 μm, surface scattered with protuberances and cavities; their size and location irregular (Fig. 6 A View Figure 6 ).

Biology.

Nymphs found under stones with coarse surfaces in slow water currents of a montane stream about 1–2 m, without direct sunlight (Fig. 7 View Figure 7 ). Adults emerged in the late afternoon. Some male imagoes were found under leaves above the stream.

Etymology.

acutata comes from the Latin adjective acutatus, indicating the shape of sharp penal apex of the new species.

Diagnosis.

The nymph of Isca acutata sp. nov. can be distinguished from other Isca species by the following characters: abdominal terga I – VIII brown, terga IX – X light brown (Fig. 1 A, C View Figure 1 ); abdominal sterna light brown (Fig. 1 B View Figure 1 ); gill VII with dorsal and ventral lamella (Fig. 1 I View Figure 1 ); posterolateral projection on segment IX (Fig. 1 B View Figure 1 ). The male imago of I. acutata sp. nov. can be distinguished by: wings translucent with cilia along posterior margin; anterior 1 / 3 of each abdominal tergum, and sterna I – VIII pale and semi-transparent; posterior 2 / 3 brown, sterna slightly lighter than terga (Fig. 3 View Figure 3 ); forceps pale; penes brown, fused basally, nib-like (Fig. 4 G View Figure 4 ).

Comparison.

Among six known species, only two species ( I. lea and I. acutata sp. nov.) have bilamellate gills VII in their nymphal stage. Those two nymphs can be differentiated by: (1) ventral setae on labrum of Isca acutata sp. nov. is less than Isca lea because it has two setal tufts (Fig. 2 A View Figure 2 ), and (2) more setae on the tip of the maxillary papa segment III of Isca acutata than Isca lea (Fig. 2 D View Figure 2 ).

In males, the new species Isca acutata sp. nov. is unique in penal shape: penes fused basally (Fig. 4 G View Figure 4 ) while those of I. purpurea , I. serendiba , I. janiceae are separated; its apical margin is straight (Fig. 4 G View Figure 4 ) while that of I. fascia is convex (Fig. 15 C View Figure 15 ); vein MA is forked less than 1 / 2 of distance from base to margin (Fig. 4 F View Figure 4 ) while vein MA of I. janiceae and I. purpurea forked more than 1 / 2 of distance from base to margin; cilia present on posterior margin of wings (Fig. 4 F View Figure 4 ) while absent in I. janiceae ; sternum IX of female Isca acutata sp. nov. cleft (Fig. 5 C View Figure 5 ) but not as deeply as I. purpurea (Fig. 12 B View Figure 12 ), while that of I. janiceae is entire.

Distribution.

China (Hainan Island).