Polyplocia orientalis Nguyen & Bae, 2003

Zheng, Xuhongyi, Qiang, Xinhe & Zhou, Changfa, 2023, First nymph-imago association in Polyploica confirming the distribution of Euthyplociidae (Ephemeroptera) in China, Deutsche Entomologische Zeitschrift 70 (1), pp. 1-11 : 1

Polyplocia orientalis Nguyen & Bae, 2003

Polyplocia orientalis Nguyen & Bae, 2003: 280.

Polyplocia orientalis : Gonçalves and Peters 2016: 554.

Redescription of mature nymphs.

See also Nguyen and Bae (2003). Body length 25.0-35.0 mm in males (n = 5), 35.0-40.0 mm in females (n = 5) (tusks included, caudal filaments excluded) (Fig. 1 ), mandibular tusks about 1/5-1/6 body length (Figs 1 , 2A ), body parts generally yellowish-brown to reddish-dark (Figs 1 , 2A-K ).

Head brownish-yellow, flattened, nearly trapezoidal, length subequal to width, slightly narrower than pronotum. Lateral ocelli pale, but with dark base, median ocellus indistinct; compound eyes round, at posterolateral corner of head, distance between compound eyes ca. 4 × each eye width. Antennae around 10.0 mm (n = 5), longer than mandibular tusks, almost glabrous; scape and pedicel subequal in length, their length slightly larger than width; anterior margin of clypeus convex (Fig. 2A ).

Mouthparts light yellow (Fig. 3A-H ), except the reddish-brown mandibular tusks. Labrum slightly concave on anterior margin, with setae along anterior and lateral margins, those on anterior margin stouter and denser, also with a tuft of longer setae on dorsal surface (Fig. 3C ). Anterolateral corner of mandibles elongated into tusks; tusks flattened, pointed at apex, 4.0-6.5 mm, ca. 3 × the head width (n = 5), densely set with setae (Fig. 3F ), divided into longer hair-like setae on both inner and outer margins which are longer near the base and stout setae on apical 1/3 of outer margin; 3-12 denticles set on outer margin of apical tusks (n = 5) (Fig. 3D ); incisor and kinetodontium each with 4 and 3 blunt denticles, respectively on left mandible, incisor with 4 blunt denticles and kinetodontium with 2 sharp denticles on right mandible (Fig. 3A, B ). Maxillae with hair-like setae on both medial and lateral margins, three canines sharp, a row of bristles present on top of crown near the canines (Fig. 3H ). Maxillary palpi three-segmented, length ratio of segments I: II: III = 1.0: 1.0: 2.0, basal segment with setae on outer margin, apical two segments surrounded by long hair-like setae (Fig. 3H ). Hypopharynx rounded, front margin concave, hair-like setae set sparsely along margins; superlinguae extended anterolaterally, with setae on margins, denser on the leading margin (Fig. 3E ). Labium: glossae and paraglossae with hair-like setae on dorsal surface, ventral surface and margins, longer and denser on margins; paraglossae expanded laterally, glossae pointed ventrally apically; labial palpi three-segmented, 2.5: 1.0: 1.6 in length, long hair-like setae present on margins of basal and apical segment and outer margin of second segment; apical segment expanded, with a row of stout setae on anteromedial margin (Fig. 3G ).

Pronotum reddish-brown with dark markings, subquadrate, lateral margins expanded slightly (Figs 1 , 2A ); anterolateral corners projected into acute points; lateral flange also extended into acute points (Figs 1 , 2A ). Mesonotum and metanotum reddish-brown, width subequal to pronotum (Fig. 1 ). Prolegs situated closely at prosternum, making the latter triangular (Fig. 1 ).

Legs yellowish-brown; foreleg longest while mid-leg shortest (Fig. 1 ). Length ratio of femora: tibia: tarsus = 1.0: 1.1: 0.6 in foreleg (Figs 1 , 2D ), 1.0: 1.0: 0.3 in mid-leg (Figs 1 , 2C ), 1.0: 0.7: 0.3 in hind-leg (Figs 1 , 2B ). Coxae and trochanters of all legs with hair-like setae on margins, mid-coxae with expanded supracoxal projections (Fig. 1 ). Femora of legs expanded, fore-femora and mid-femora densely covered with both short spine-like setae and long hair-like setae on margins and dorsal surface, hind-femora with hair-like setae on outer margin, but very sparse setae on inner margin and dorsal surface (Fig. 2B-D ); hind-femora with subapical setae patch on ventral surface (Fig. 2G ). Fore- and mid-tibiae with an apical, triangular, pyramidal spine or spur overlapping tarsi to about 1/3 of tarsal length (larger on fore-tarsi), margins with bristle-like setae (Figs 1 , 2I ); fore- and mid-tibiae with hair-like setae on both margins, some short spine-like setae at apex; hind-tibiae with sparse hair-like setae (Fig. 2B ); mid-tibiae with clear patello-tibial suture. Fore-tarsi with a sharp apical projection covering claw, with hair-like setae on margins and dorsal surface, additional spine-like setae on margin and projection (Fig. 2H ); mid-tarsi with hair-like setae and a row of short spine-like setae dorsally (Fig. 2C ); hind-tarsi with sparse hair-like setae. Claws stout and hooked (Fig. 2H ).

Abdomen dark brown with light markings, including a pale mid-line, two pairs of pale medial dots and two pairs of lateral pale dots on each tergum, median pairs of dots progressively shortening from anterior to posterior segments (Fig. 2J ); sterna light to pale brown (Fig. 2K ). A pair of gills on abdominal segments I-VII (Fig. 1 ); gills I light grey, smaller than others (less than 2 mm), divided into two lobes, dorsal lobe larger and expanded distally, about 1.5 × length of ventral one (Fig. 2E ); gills II-VII similar, light to dark grey, bifurcated at base, dorsal lamella slightly shorter than ventral lamella, both lamellae slender and fringed with hairs (Fig. 2F ). Terminal filament sub-equal to body length, cerci ca. 3/5 of body length (Fig. 1 ), all with short spine-like setae on articulations and hair-like setae on both margins, progressively shorter from base to apex.

Description of male imagoes.

Body length 16.0-18.0 mm (n = 3) (Fig. 4A ). Head dark brown, compound eyes black, width between eyes subequal to eye width (Fig. 4B ). Three ocelli white, but with dark basal band, rounded, medial one smallest. Antennae sub-equal to head width, scape and pedicel stout, dark brown, flagella filamentous, light brown (Fig. 4B ). Pronotum yellowish-black with light markings, nearly trapezoidal in dorsal view, length sub-equal to width, lateral and posterior margins ridged, posterior one slightly wider than head (Fig. 4B ). Mesonotum and metanotum yellowish-brown (Fig. 4B ).

Forewings 19.0-22.0 mm, hindwings 7.0-8.0 mm (n = 3) (Fig. 5A-C ). Forewings translucent, base, costal and subcostal areas tinged brown (Fig. 5A ); longitudinal veins light to dark brown; forking point of MA at about 1/3 distance from base to margin, same level as fork of Rs; MP forked near base. Two longitudinal intercalaries (ICu) share a common stem attaching to CuP, some sigmoid veins originating from posterior ICu going to hind-margin; CuP and A1 also with veinlets connecting them to hind-margin of wing (Fig. 5A ). Hindwings hyaline, but with pigmented base; costal process round; Rs forked at about 1/3 distance from base to margin, MP forked at about 1/4 distance from base to margin, MA simple; anal region with some veinlets directed towards margin (Fig. 5B, C ).

Legs grey to light brown with dark markings, femora of all legs with pale base, tarsi paler than tibiae (Fig. 6A-C ). Forelegs sub-equal to body length, hind-legs longer than mid-legs (Fig. 6A-C ). Femora: tibiae: tarsi = 1.0: 1.5: 1.3 in forelegs (Fig. 6A ), 1.0: 1.1: 0.3 in mid-legs (Fig. 6B ), 1.3: 1.0: 0.3 in hind-legs (Fig. 6C ). Ratios of tarsomeres I: II: III: IV: V in forelegs = 1.0: 15.0: 12.5: 10.0: 7.0 (Fig. 4A ); mid- and hind-tarsi four-segmented, length ratio of tarsomeres = 1.0: 1.0: 1.0: 3.0 (Fig. 6B, C ). Claws paired, fore-claws lamellar-shaped, a very small hook present apically (Fig. 6D ). Mid- and hind-claws similar, sharply hooked (Fig. 6E ).

Abdomen grey to brown dorsally, with light markings as in larvae, two pairs of pale dots on each segment, lateral margins pale (Fig. 4B ). Styliger plate yellowish-brown, posterior margin straight (Fig. 7A ). Forceps yellowish-brown with a dark marking near apex, about 3.5 mm (n = 3), one segmented, slender and cylindrical, but flattened apically, about 4 × length of penis (Fig. 7A, B ). Penis yellowish with dark shading, flattened; basal 2/3 fused together, apical 1/3 divided with a V-shape cleft; each lobe has a deep apical depression and extended apico-laterally into beak-like structure, margins sclerotised (Fig. 7C, D ). Caudal filaments grey brown, about 3 × body length, some short setae on surface (Fig. 4A, B ).

Description of female subimagoes

. Body length 28 mm, similar to female imago, except dorsal surface and lateral margin of pronotum smooth, length/width of pronotum larger in female subimago than in imago, scutellum more protruded (Fig. 8A ).

Description of female imagoes.

Colour pattern, veins and other characters similar to male. Body length 26.0 mm (Fig. 8B ). Head dark, compound eyes black, width between eyes about 2 × width of each eye (Fig. 8B ). Ocelli white, rounded, medial ocellus smallest. Pronotum black with light markings, corrugated in dorsal view. Mesonotum yellowish-brown, scutellum slightly protruded. No obvious sexual dimorphism on wings.

Legs brownish-grey, Femora: tibiae: tarsi = 1.0: 1.2: 0.8 in forelegs (Fig. 8C ), 1.0: 1.0: 0.3 in mid-legs (Fig. 8D ), 1.3: 1.0: 0.3 in hind-legs (Fig. 8E ). Tarsomere I: II: III: IV: V in forelegs = 1.0: 4.0: 2.0: 1.5: 2.0 (Fig. 8C ); length ratio of mid- and hind-tarsomeres = 0.7: 1.0: 1.0: 1.0: 2.8 (Fig. 8D-E ). Claws paired, all claws similar, sharply hooked.

Abdomen dark brown dorsally, with light markings as in male imagoes, with four pairs of light dots and a light mid-line on each segment (Fig. 8B ). Posterior margin of sternum VII and subanal plate smooth, not obviously protruding or cleft (Fig. 8B ).

Description of eggs.

Dissected from female imago, barrel-shaped, smooth without apparent polar cap or ridges (Fig. 9 ).

Distribution.

China (Yunnan Province), Vietnam (Dak Lak Province, Lam Dong Province, Thua Thien Hue Province).

Diagnosis.

The mature nymphs of Polyplocia orientalis are characterised by a large body (25.0-40.0 mm) and long mandibular tusks (4.0-6.5 mm) (Fig. 1 ), acute anterolateral apex of pronotum (Fig. 2A ), uniformly pale abdominal sterna (Fig. 2K ) and apically expanded dorsal lobe of gill I (Fig. 2E ). Their imagoes can be easily recognised by transparent wings (Fig. 4A ), smooth eggs in females (Fig. 9 ) and T-shaped male penis with apical depression on both lobes (Fig. 7A-D ).

Gonçalves and Peters (2016) examined specimens of almost all known Polyplocia species and provided details of their comparison. We use their information as the basis of this comparative discussion.

The males of P. orientalis resemble P. vitalisi in most characters. Both have transparent wings (except costal and subcostal sections of forewings), two intercalaries between CuA and CuP, cross-veins without surrounding clouds (Fig. 5 ). There are two differences between them: 1) body size of the P. orientalis is 16.0-18.0 mm, while that of P. vitalisi is around 12 mm; 2) the penis lobes of P. orientalis are extended laterally and pointed with deeply concave lateral margins (Fig. 7 ), but the penis lobes of the P. vitalisi are almost straight.

Males of P. campylociella have penis lobes similar to P. vitalisi . However, the cross-veins of forewings are pigmented and the membrane has a brown tinge. It can be differentiated from P. orientalis easily.

The males of P. nebulosa have pigmented cross-veins, both the abdominal terga and sterna have distinct brown markings. Further, its penis lobes are almost entirely fused with a very shallow emargination between the two lobes. In contrast, the males of P. orientalis , described in the present study, have clear wings (Fig. 5 ), somewhat uniform abdominal color (except terga with two pairs of pale dots) (Fig. 4B ) and slimmer penial lobes (Fig. 7 ).

Nymphs of P. orientalis and the possible nymph of P. nebulosa are very similar to each other. Only three points are found to separate them. First, in mature nymphs, the lateral margins of the pronotal flanges of P. nebulosa are almost straight and parallel to the margin of the pronotum, the anterolateral corner tapers abruptly forming a relatively blunt apex; while those of P. orientalis are slightly sinuous and the anterolateral corner tapers gradually forming a more acute apex (Fig. 2A ). Second, the dorsal lobe of the first pair of gills of P. nebulosa have nearly parallel lateral margins but those of P. orientalis have an apically expanded larger lobe (Fig. 2E ). Third, the abdominal sterna of P. nebulosa have brown markings, while those of P. orientalis lack such markings (Fig. 2K ). In addition, their eggs are different: eggs of P. nebulosa have mesh with raised ridges, while eggs are smooth and glabrous in P. orientalis .

The nymphs of P. campylociella were only tentatively associated and have not been confirmed, not being discussed here.

Genetic identity.

Morphologically, our Chinese nymphal specimens match perfectly with the original description of P. orientalis given by Nguyen and Bae (2003) and some figures provided by colleagues. To ensure our identification, we also sequenced the COI gene of our specimen. The K2P genetic distance is 0.10 between our sequence (GenBank accession number OP962407) and a sequence stored in the GenBank of P. orientalis (GenBank accession number OP347109.1).

Biological notes.

Nymphs were found in small forested streams narrower than 0.6 m, some sections of the stream had almost no flow, width less than 0.2 m and depth 1-15 cm. Nymphs of different instars were found at the same time (length from 0.5-40 mm), hidden in mud under stones (Fig. 10 ). Imagoes were collected at night sporadically, the rest on nearby vegetation. Judging from all the available information, it is assumed to be a univoltine and highly asynchronous population.

Figures

Figure 1. Nymphal habitus of Polyplocia orientalis from China. Scale bar: 5.0 mm.

Figure 2. Nymph of Polyplocia orientalis from China A Head and prothorax; B Hind-leg; C mid-leg; D Foreleg; E Gill I; F Gill IV; G Hind-leg (ventral view); H Fore-tarsus and claw; I Apex of fore-tibia; J Abdomen (dorsal view); K Abdomen (ventral view). Scale bars: 1.0 mm (A-D, F, G, I-K); 0.1 mm (E, H).

Figure 3. Nymphal mouthparts of Polyplocia orientalis from China A Right mandible (ventral view); B Left mandible (ventral view); C Labrum (dorsal view); D Apex of mandibular tusk; E Hypopharynx (ventral view); F Right mandible (dorsal view); G Labium (ventral view); H Left maxilla (ventral view). Scale bars: 0.5 mm.

Figure 4. Male imago of Polyplocia orientalis from China: A Lateral view; B Dorsal view. Scale bars: 5.0 mm.

Figure 5. Wings of male Polyplocia orientalis from China: A Forewing; B Posterior area of hind-wing; C Hind-wing. Scale bars: 5.0 mm (A, C); 1.0 mm (B).

Figure 6. Legs of male Polyplocia orientalis from China: A Foreleg; B Mid-leg; C Hind-leg; D Claw of foreleg; E claw of mid-leg. Scale bars: 1.0 mm (A-C); 0.1 mm (D, E).

Figure 7. Genitalia of Polyplocia orientalis from China A Ventral view; B Detail of forceps (ventral view); C Penis (ventral view); D Penis (dorsal view). Scale bars: 0.5 mm.

Figure 8. Females of Polyplocia orientalis from China A Female subimago, dorsal view; B Female imago, dorsal view; C Foreleg of female imago; D Mid-leg of female imago; E Hind-leg of female imago. Scale bars: 2.0 mm (A-B); 1.0 mm (C-E).

Figure 9. Egg of Polyplocia orientalis from China. Scale bar: 0.05 mm.

Figure 10. Habitat of Polyplocia orientalis nymphs from China.