Isca acutata Gong & Zhou, 2025, sp. nov.
Creators: name: Gong, De-Wen
name: Zhou, Chang-Fa
Publisher: name: Zenodo
Year: 2025
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Ephemeroptera
Leptophlebiidae
Isca
Isca acutata

description: Isca acutata sp. nov.
Figs 1, 2, 3, 4, 5, 6 A
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. Paratypes • 1 male imago (reared from nymph) and 10 nymphs, same data as holotype.
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. • 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. • 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. • 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.
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). 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).
Head: prognathous, area between three ocelli darker than others (Fig. 1 A, C).
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).
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). 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). 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). 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).
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). 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). Claw with 14 denticles, distal one larger than others, proximal four denticles smaller (Fig. 1 G).
Abdomen: posterior margin of each tergite with contiguous acute spines, posterolateral projections on segment IX only (Fig. 1 A – C). Gills present on segments II to VII of ventral side of abdomen (Fig. 1 B). Gills similar morphologically, consist of two slender and unbranched lamellae, gills progressively smaller from anterior to posterior (Fig. 1 H – I). 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).
Male imago (in alcohol): Body length 4.4 mm, generally amber to brownish, wings deep brown (Fig. 3).
Head: Width between two compound eyes about half of one eye width; upper half of it orange, lower half black (Fig. 4 A).
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). Claw dissimilar, one hooked, one blunt (Fig. 4 E).
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).
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). 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). Caudal filaments pale (Figs 3 A, 4 G).
Female: body length 4.1 mm, caudal filaments brown with spine-like setae. Coloration similar to male, sternum IX slightly concave apically (Fig. 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).
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). 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); abdominal sterna light brown (Fig. 1 B); gill VII with dorsal and ventral lamella (Fig. 1 I); posterolateral projection on segment IX (Fig. 1 B). 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); forceps pale; penes brown, fused basally, nib-like (Fig. 4 G).
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), and (2) more setae on the tip of the maxillary papa segment III of Isca acutata than Isca lea (Fig. 2 D).
In males, the new species Isca acutata sp. nov. is unique in penal shape: penes fused basally (Fig. 4 G) while those of I. purpurea, I. serendiba, I. janiceae are separated; its apical margin is straight (Fig. 4 G) while that of I. fascia is convex (Fig. 15 C); vein MA is forked less than 1 / 2 of distance from base to margin (Fig. 4 F) 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) while absent in I. janiceae; sternum IX of female Isca acutata sp. nov. cleft (Fig. 5 C) but not as deeply as I. purpurea (Fig. 12 B), while that of I. janiceae is entire.
Distribution.
China (Hainan Island).
description: Published as part of Gong, De-Wen & Zhou, Chang-Fa, 2025, Review of the genus Isca (Ephemeroptera, Leptophlebiidae) from China with a new species and a new species record, pp. 239-258 in ZooKeys 1234 on pages 239-258, DOI: 10.3897/zookeys.1234.140905