Isonychia latias, Mu & Huang, 2024

Mu, Pengxu & Huang, Xiaolei, 2024, Discovery of a new Isonychia species with distinctive characters from southwestern China, and preliminary exploration of its phylogenetic status (Ephemeroptera, Isonychiidae), ZooKeys 1218, pp. 113-129 : 113-129

Isonychia latias sp. nov.

Figs 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 Chinese name: 比翼等蜉

Type material.

Holotype: male imago, China • Guizhou Province, Zunyi City, Xishui County, China Dan Xia Valley , Sanchahe River [贵州省遵义市习水县中国丹霞谷三岔河] (28.497144 N, 106.410003 E, alt. 880 m), 21.V.2024, leg. Pengxu Mu; in ethanol; FAFU . Paratypes • 8 male imagos, 8 female imagos, 12 male subimagos, 15 female subimagos, 12 larvae, 22 larval exuviae, same information as holotype; in ethanol; FAFU .

Description.

Male imago. Forewing length 18.5–20.0 mm.

Coloration. General body color brown to reddish brown (Fig. 1 A ). Head capsule dark brown except anterior part pale; compound eyes gray (Fig. 2 A ). Pronotum dark brown except posterolateral parts pale; mesoscutum brown, and mesoscutellum and metanotum dark brown; pleura of pterothorax with three yellowish stripes formed by pale conjunctivas; basisternum and furcasternum of mesothorax dark reddish brown, and basisternum of metathorax pale reddish (Fig. 2 B, C ). Forefemur brown, slightly shaded with dark brown apically; foretibia and foretarsus dark brown; mid- and hindlegs brown (Fig. 2 G ). Fore- and hindwings with distinct, dark brown coloration and pale yellowish shadings as in Fig. 3 A ; all veins of both wings pale brown. Abdominal terga I and X dark brown; terga II – VII pale brown, except lateral margins slightly shaded with dark brown; terga VIII – IX with anteromedian part pale brown and posterolateral part dark brown, and dark brown area of tergum IX larger than that of tergum VIII; terga II – IX with pair of dark, submedian, longitudinal, oblique stripes (Fig. 4 A ). Abdominal sterna reddish brown except sternum IX dark brown; sterna II – IX with pair of dark submedian longitudinal oblique stripes, and sterna II – VI with four dark dots situated in transverse line behind these stripes. Styliger and gonostyli pale brown, and penis dark brown (Fig. 4 C ). Cerci dark brown along their entire length.

Legs (Fig. 2 G ). Foreleg: length ratio of femur (2.7 mm): tibia: tarsus 1.0: 1.5: 1.6, length ratio of tarsomeres from basal to apical 1.0: 1.3: 1.0: 0.9: 0.4. Midleg: length ratio of femur (3.2 mm): tibia: tarsus 1.0: 1.4: 0.6, tarsomeres arranged in decreasing order as 5, 2, 1, 3, 4. Hindleg: length ratio of femur (3.2 mm): tibia: tarsus 1.0: 1.2: 0.5, tarsomeres arranged in decreasing order as 5, 2, 1, 3, 4. Foreleg with both claws similar, blunt, and provided with a soft plate; mid- and hindlegs with both claws similar and pointed.

Wings (Fig. 3 A ). Forewing: number of crossveins relatively large, and pterostigmatic area with about 30 crossveins between C and Sc; MP forked asymmetrically, MP 2 strongly curved in proximal part; cubital field with two or three unforked and four forked veins gone from CuA to basitornal and tornoapical margins. Hindwing: length ratio of maximum length: width 1.4: 1.0; costal projection round and with 4–5 crossveins; tornoapical margin slightly concave; RS forked about 1 / 2 of distance from base of vein to margin; MA forked slightly more apically than RS; MP forked about 3 / 4 of distance from base of vein to margin.

Genitals (Fig. 4 C, E – H ). Gonostyli pedestals relatively long with blunt ventral-apical-median angles. Gonostylus with length of segment II ca 2.0 of segment III length, and length of segment III ca 1.4 of segment IV length. Penis reaching to middle part of gonostyli pedestals; penis lobes deeply separated with apices strongly divergent, and stout spines only present on subapical area of ventral surface. Processes between styliger and penis absent.

Female imago. Forewing length 22.7–23.5 mm. Similar to male imago except the following:

Coloration. General body color reddish (Fig. 1 B ). Compound eyes blue-gray (Fig. 2 D ). Thoracic pattern similar to male imago but reddish in general (Fig. 2 E, F ). Forefemur reddish, slightly shaded with dark reddish apically; foretibia dark reddish; foretarsus, mid- and hindlegs reddish (Fig. 2 H ). Forewing with dark brown band occupying pterostigmatic area; hindwing colorless; all veins of both wings dark brown (Fig. 3 B ). Abdominal tergum I dark reddish; terga II – VII reddish; terga VIII – IX with anteromedian part reddish and posterolateral part black, and black area of tergum IX larger than that of tergum VIII (Fig. 4 B ). Abdominal sterna reddish brown, except sternum IX with large, transverse, dark brown band (Fig. 4 D ).

Legs (Fig. 2 H ). Foreleg: length ratio of femur (2.8 mm): tibia: tarsus 1.0: 1.5: 0.9, length ratio of tarsomeres from basal to apical 1.0: 1.1: 0.9: 0.7: 1.1. Midleg: length ratio of femur (3.5 mm): tibia: tarsus 1.0: 1.3: 0.5. Hindleg: length ratio of femur (3.8 mm): tibia: tarsus 1.0: 1.0: 0.4. Both claws of all legs similar and pointed.

Wings (Fig. 3 B ). Hindwing: length ratio of maximum length: width 1.6: 1.0; RS forked about 2 / 5 of distance from base of vein to margin; MA forked about 1 / 2 of distance from base of vein to margin; MP forked about 7 / 10 of distance from base of vein to margin.

Genitalia (Fig. 4 D ). Subgenital plate slightly elongated with rounded posterior margin. Subanal plate with deep posteromedian emargination.

Male subimago. Similar to male imago except the following: Mesonotum with brown lateral pigmented area occupying submedioscutum and sublateroscutum back to posterior scutal protuberance (PSp); medioscutum and PSp pale. Foreleg: length ratio of femur (2.6 mm): tibia: tarsus 1.0: 1.4: 1.2, length ratio of tarsomeres from basal to apical 1.0: 1.0: 0.8: 0.7: 0.7. Tarsomeres of all legs covered with “ U ” - shape, blunt microlepides. Both claws of all legs similar and pointed. Wings brown to dark brown in general, coloration as in Fig. 3 C .

Female subimago. Similar to male subimago except the following: Foreleg: length ratio of femur (2.9 mm): tibia: tarsus 1.0: 1.4: 0.9, length ratio of tarsomeres from basal to apical 1.0: 1.1: 0.9: 0.7: 1.1. Subgenital plate not elongated.

Larva. Body length: male 19.3–20.6 mm; female 23.7–26.1 mm.

Coloration. General body color dark brown. Head capsule dark brown, except frontal carina, and median parts of clypeus and vertex yellowish; scape and pedicel brown, flagella pale; dorsum of labrum dark brown with pale longitudinal line medially (Fig. 5 A ). Thoracic nota dark brown but with pale median longitudinal stripe and irregular pale markings (Fig. 6 A ). Forefemur with two transverse dark bands, foretibia with 1 transverse dark band medially, and foretarsus with 1 transverse dark band in proximal part; mid- and hindleg with similar coloration except femur with two transverse dark bands connected by dark stripe, and dark band on tibia more basally (Fig. 6 C ). Abdominal terga dark brown in general; terga I – VII with pale median longitudinal stripes (shorter and less pronounced posteriorly); terga II – IX with pair of pale submedian longitudinal stripes; tergum X with pair of light spots close to anterior margin (Fig. 7 C ). Abdominal sterna brown in general; sterna II – IX with pair of pale submedian longitudinal stripes, and sterna II – VIII with four dots situated in transverse line behind these stripes. Tergalii without distinct dots or markings (Fig. 7 A ). Caudalii brown basally and gradually paler towards apices without dark band medially.

Mouthparts (Fig. 5 B – F ). Typical of Isonychia , setal pattern consistent with other congeners in general. Labrum subquadrate, widest part about twice as long. Superlingua round, width ca 0.6 of lingua width. Distal dentiseta of maxilla strongly diminished, needle-like, distinctly shorter and slenderer than proximal dentiseta. Length of segment I of maxillary palp ca 0.4 of segment II length. Length of segment I of labial palp ca 0.5 of segment II length. Length of paraglossa ca 0.5 of glossa length.

Legs (Fig. 6 C – E ). Setal pattern typical of Isonychia . Ventral cleft of hind femur with 5–8 spines. All claws with 7–9 blunt denticles. Gill on joining of forecoxa with thorax well developed, tuft-like.

Thoracic sterna (Figs 6 B , 7 B ). Bifurcate projection on basisternum of mesothorax well developed; paired projections on basisternum of metathorax relatively weakly expressed.

Tergalii (Fig. 7 A ). Lamella of tergalius I distinctly smaller than other lamellae of tergalii, apical part of costal rib with 4–5 spine-like denticles; lamellae of tergalii II – VII gradually larger posteriorly, each lamella usually with 5–7 spine-like denticles on apical part of costal rib and on apical part of posterior branch of anal rib (rarely beyond this range, and in tergalii III – VII mostly with 6 denticles), and no denticles present on apical margin between these two areas. Ventral fibrillose lobe well developed in all tergalii.

Abdominal terga and sterna (Fig. 7 C, D ). Terga II – X with acute denticles along posterior margins. Sterna VI – VIII with acute denticles along posterior margins, and subanal plate with smaller and denser denticles on median part of posterior margin. Posterolateral spines well developed on segment VIII – IX.

Egg (Fig. 8 A – D ). Spherical; chorion densely covered with small tubercles, and without reticulation; KCTs dense in one hemisphere, and other area sparsely scattered with smaller KCTs.

Diagnosis.

Isonychia latias sp. nov. can be readily distinguished from its congeners by the following combination of characters: For male imago: A) wings with distinct, dark brown coloration: on forewing occupying a large area of apical half as a transverse band, a small area around bifurcation point of Rs, and edges along basitornal margin and tornus, and on hindwing occupying almost whole apical part; B) mid- and hindlegs brown, nearly consistent with forefemur; C) pleura of pterothorax with three yellowish stripes formed by pale conjunctivas. For larvae: A) lamellae of all tergalii without spines on apical margin, and without distinct dots or markings; B) abdominal terga I – VII with pale median longitudinal stripes, terga II – IX with pair of pale submedian longitudinal stripes, and tergum X with pair of light spots close to anterior margin; C) caudalii brown basally and gradually paler towards apices without dark band medially. The larvae of I. latias sp. nov. resemble those of I. fuscimarginata Qiang et al., 2024 , based on the similar coloration of abdominal terga. However, they can be differentiated by the following characters: A) each lamella of tergalii of I. fuscimarginata with a large middle dark purple dot basally, while those of I. latias sp. nov. without dots; B) ventral fibrillose lobes of tergalii of I. fuscimarginata with fewer filaments than those of I. latias sp. nov.; C) I. fuscimarginata with submedian dark band on all caudalii and apical dark band on cerci, while all caudalii of I. latias sp. nov. without dark band along their entire length.

Distribution.

China: Guizhou Province (Zunyi City, Sanchahe River).

Etymology.

The new species is named after Latias, an alate Pokémon with red and white appearance. The specific epithet latias is treated as a noun in apposition to the generic name.

Biology.

The larvae of Isonychia latias sp. nov. have so far been found only in the Sanchahe River in Guizhou Province. The collection site is located near a Danxia landform, characterized by a large amount of dark red rocks in the river (Fig. 9 A, B ). The larvae were primarily collected in rapid sections, and one mature larva about to emerge was found in a gravelly shallow area (Fig. 9 C, D ). The exuviae of the larvae were mainly found on stones 10–20 cm above the water surface, with the highest reaching more than 50 cm. The subimagos of both sexes moulted into imagos spending three nights after they were caught.

Genetics

We performed a multi-gene phylogenetic analysis using the mitochondrial genes COI and 16 S, including our new species, four Isonychia s. s. species, and one Prionoides species (Table 2 ). Chromarcys magnifica Navás, 1932 and Paegniodes cupulatus ( Eaton, 1871) were used as outgroups. The topology of the ML tree shows that Isonychia (Prionoides) shima ( Matsumura, 1931) is the first species to branch out, forming a sister group with the remaining species. Within the remaining species, our new species is the first to split off, forming a sister group with the other four Isonychia s. s. species, which form a monophyletic group (Fig. 10 ).

Figures

Figure 1. Adults of Isonychia latias sp. nov. A male imago B female imago C male subimago. (Photographed by Qianle Lu).

Figure 2. Imaginal structures of Isonychia latias sp. nov. A – C male imago A head B thorax, lateral view C thorax, ventral view D – F female imago D head E thorax, lateral view F thorax, ventral view G, H legs (fl: foreleg; ml: midleg; hl: hindleg) G male imago H female imago. Scale bars: 1.0 mm (A, D, G, H).

Figure 3. Wings of Isonychia latias sp. nov. A male imago B female imago C male subimago. Scale bars: 5.0 mm.

Figure 4. Imaginal structures of Isonychia latias sp. nov. A, B abdominal segments V – X, dorsal view A male B female C, D genital segments, ventral view C male D female E – H penis E ventral view F dorsal view G penis lobe enlarged, ventral view H penis lobe enlarged, dorsal view.

Figure 5. Larval structures of Isonychia latias sp. nov. A head, front view B labrum (left: dorsal view; right: ventral view) C mandible, dorsal view (left: left mandible right: right mandible) D hypopharynx (left: dorsal view right: ventral view) E maxilla, dorsal view F labium (left: dorsal view; right: ventral view).

Figure 6. Larval structures of Isonychia latias sp. nov. A right half of pronotum and mesonotum B thorax, ventral view (white arrow shows projection on basisternum of mesothorax black arrow shows projection on basisternum of metathorax) C legs (fl: foreleg ml: midleg hl: hindleg) D apical part of foreleg E ventral cleft of hindfemur. Scale bar: 1.0 mm (C).

Figure 7. Larval structures of Isonychia latias sp. nov. A tergalii (t 1: tergalius I; t 4: tergalius IV; t 5: tergalius V; t 7: tergalius VII) B thoracic sterna, lateral view (white arrow shows projection on basisternum of mesothorax black arrow shows projection on basisternum of metathorax) C abdominal terga I – X D abdominal sterna VIII – IX E caudalii. Scale bars: 1.0 cm (A); 2.0 mm (C, E).

Figure 8. SEM photos of eggs of Isonychia latias sp. nov. A, B egg C micropyle enlarged D KCTs enlarged.

Figure 9. Habitat of Isonychia latias sp. nov. A, B Sanchahe River, Dan Xia Valley, China C, D mature larva of Isonychia latias sp. nov. about to emerge in natural environment.

Figure 10. ML tree for Isonychia spp based on concatenated sequences of two genes (COI and 16 S) showing Prionoides (green) and Isonychia s. s. (red). ML bootstrap values above 70 are indicated next to the nodes.