Epeorus ( Proepeorus ) falcatus, Ma & Lei & Li & Zhou, 2021

Epeorus ( Proepeorus) falcatus sp. nov. Zhou

Figs 7–9 View Figure 7 View Figure 8 View Figure 9 , 10C–D, G–H View Figure 10 , 11E–H View Figure 11 , 12B View Figure 12 , 13D–E View Figure 13 , 14C–D View Figure 14 , 15H View Figure 15 , 16H View Figure 16

Materials examined

Holotype: male imago, Wudong Village ( 26°22′55.4″N, 108°10′01.8″E), Leishan County, Guizhou Province, collected by Zhen-Xing MA, Xu-Hong-Yi ZHEN, 1–5-VIII-2019 GoogleMaps . Paratypes: 3 male imagoes 2 female imagoes 10 nymphs, same as holotype; 5 nymphs, Huaping Nature Reserve, Guangxi Province, collected by Zhen-Xing MA, 20-21-VIII-2020; 30 nymphs, Jintong Mountain, Shaoyang City, Hunan Province, collected by Zhen-Xing MA, 23-VIII-2020.

Nymph (in ethanol). Body length 10.0–12.0 mm (female), 8.5–9.5 mm (male), caudal filaments 14.0–15.0 mm (female), 11.0 mm (male). Body generally pale to brown ( Figure 7 View Figure 7 (a)).

Head. ellipsoid, head width/length ratio 1.39, anterior and lateral margins evenly convex, posterior margin slightly convex (nearly straight); anterior margin with a row of dense setae directed anteriorly, posterior margin with two tufts of setae. Head generally pale, with median brown or dark grey irregular markings ( Figures 7 View Figure 7 (c) and 9 (a)). Labrum: lateral margins straight and widened anteriorly, anterior margin with a distinct median notch, dorsal surface with 6 bristles antero-medially and 2 bristles near each side of anterolateral margin. Ventral surface with a row of bristles along lateral margin extend to anterior margin and brush of fine setae medially ( Figures 8 View Figure 8 (a) and 9(b)). Mandibles: outer incisor with 2 (left mandible) or 3 (right mandible) apical lobes and serrated margins, inner incisor with 2 (right mandible) or 3 (left mandible) apical lobes and serrated outer margins. Prostheca represented by a tuft of plumose setae ( Figures 8 View Figure 8 (b,c) and 9(c,d)). Maxillae: with 1 fimbriated setae at base of apex of maxilla ( Figure 15 View Figure 15 (h)); basal segment of maxillary palp slightly expanded proximally and with a tuft of (4–5) distal bristles on outer margin; apical segment 1.35× length of basal segment, with slender basal half and extremely expanded distal half ( Figure 8 View Figure 8 (e)). Hypopharynx: lingua with anterolateral lobes ( Figure 8 View Figure 8 (d)). Labium: with narrow U-shaped separation between glossae; glossa triangular, with a shallow subapical projection, dorsum with a row of longitudinal dense setae, both inner margin and outer margin of glossa with a row of bristles; apical segment of labial palpi slightly shorter than basal segment, apical/basal segment length ratio 0.86 ( Figures 8 View Figure 8 (f) and 9(e)).

Thorax. pale to brown with irregular markings. Femora pale, with a medial dark spot (indistinct in some individuals) and irregular brown markings, outer margin with a row of long setae and sparse short setae ( Figure 7 View Figure 7 (f)), dorsum with scattered blunt spatulate and arrow-like setae ( Figure 9 View Figure 9 (f)). Proximal and medial portion of tibiae slightly darkened, base and apex of tarsi darkened ( Figure 7 View Figure 7 (f)). Forefemora/foretibiae length ratio 0.96, mid femora/mid tibiae length ratio 1.08, hind femora/hind tibiae length ratio 1.22. Claws with 3 subapical denticles ( Figure 9 View Figure 9 (g)).

Abdomen. Pale with brown markings. Terga segments II–IX with paired small submedian spines and a median longitudinal dark stripe. Terga II–IV with paired submedian irregular pale spots. Each tergum with transverse brown band along anterior margin ( Figure 7 View Figure 7 (a,d)). Posterior margins of terga with blunt denticles and mixed with smaller round pointed denticles ( Figure 9 View Figure 9 (h)). Sterna colourless (sterna VII–IX with paired brown stripes in some individuals) ( Figure 7 View Figure 7 (e)). Gills: gill I moderately expanded anteriorly and narrowed apically, outer margin with a row of fine setae ( Figure 9 View Figure 9 (i)); gills II– VI similar, distal half of costal margin with a row of long setae ( Figure 9 View Figure 9 (j)); gill VII oval, with long anal rib, slightly curved and without distinct fold ( Figures 7 View Figure 7 (e) and 9(k)). Cerci pale to brown, with a row of dorsal setae along basal segments.

Male imago (in ethanol). Body length 9.0–10.0 mm, forewing 9.5–10.0 mm, hindwing 3.0– 3.5 mm, cerci 28.0–34.0 mm. Body generally brownish ( Figure 10 View Figure 10 (c)).

Head. Face fold dark brown, antennae brown, median area brown. Compound eyes pale (dark brown when alive), contiguous, with darker basal half ( Figure 10 View Figure 10 (g)).

Thorax. Dark brown. Prosternum dark brown, median depression of mesothoracic furcasternum convergent anteriorly ( Figure 10 View Figure 10 (h)). Most area of wings transparent except semi-hyaline stigma area. Forewings with brown veins and dark brown costal brace, stigma region with 9–10 cross veins between Sc and C; MA forked 2/3 of distance from base to margin, MP forked 1/3 of distance from base to margin; hindwings transparent, MP forked 1/2 of distance from base to margin ( Figure 10 View Figure 10 (d)).

Legs. Forelegs brown, with dark brown tibiae and distal half of femora, paler basal half of femora and tarsi, ratios of femora: tibiae: tarsi = 2.5: 3.2: 5.5, order of tarsal segments arranged in descending order: 1, 2, 3, 4, 5. Middle legs light brown, ratios of femora: tibiae: tarsi = 2.2: 2.1: 1.3, order of tarsal segments arranged in descending length 1, 2, 3, 5, 4 (hind legs missing). Femora of all legs with a median dark brown macula. Claws of each leg dissimilar, one blunt, one hooked.

Abdomen. Light brown, with darker maculae. Terga II–IX with similar colour pattern ( Figure 11 View Figure 11 (e)): indistinct brown transverse band along anterior margin; median area brown, with a longitudinal median dark stripe and a pair of paler irregular maculae (like the fusion of two dots); posterior half of each tergum darker and with a dark brown transverse band along posterior margin extended to lateral margin. Tergum X pale, with a median dark stripe. Colouration of sterna II–VIII similar ( Figure 11 View Figure 11 (f)): 1) dark brown median band; 2) a pair of distinct brown oblique stripes near anterior margin (medio-anterior myo-sigilla, progressively fading posteriorly); 3) a pair of small round blanks inside the median band (medio-posterior myo-sigilla). Sternum IX brown, with longitudinal dark band laterally; styliger light brown, posterior margin slightly convex medially. Forceps segments I–II brown, III light brown and IV pale, combined length of segments III–IV subequal to half of segment II; penis lobes widely divergent, with sharp lateral hooked tips directed dorsally and medio-apical emargination. Submedian titillators distinct ( Figures 12 View Figure 12 (b), 13(d,e)). Cerci with dark annulations.

Female imago. Body length 10.5 mm, forewing 10.5 mm, hindwing 3.5 mm, cerci 20.5 mm. General reddish-brown, colouration of body similar to male imago. Thorax paler than in male, wings same as male. Length ratios of femora: tibiae: tarsi of fore legs = 2.6: 2.6: 2.1; length ratios of femora: tibiae: tarsi of middle legs = 2.7: 2.6: 1.3; length ratios of femora: tibiae: tarsi of hind legs = 3.0: 2.5: 1.1. Colour pattern of abdominal terga same as male imago but darker ( Figure 11 View Figure 11 (g)). Abdominal sterna somewhat different to male imago ( Figure 11 View Figure 11 (h)): sterna VII–IX darker than other segments. Subgenital plate extended to posterior margin of sternum VIII and with rounded posterior margin, sternum IX with shallow median emargination ( Figure 14 View Figure 14 (c,d)).

Etymology

The Latin specific name falcatus means sickle-shaped, curved or hooked, refers to the sickle-shaped gill I of nymph.

Biology

Nymphs of this species occur in the small-sized mountain streams (1.0–3.0 m wide, 0.1– 0.5 m deep, ca. 1000–1300 m a.s.l.), and they are found underneath stones in moderately flowing sections where the substrate is mostly stony. Moulting of the subimago was observed in 7:30 PM, and the process lasts ca. 4 minutes.

Diagnosis and remarks

This species can be recognised by the following diagnosis characters. In the adult: 1) penis lobes with lateral hooked projections and distinct median titillators ( Figure 13 View Figure 13 (d)); 2) subgenital plate of female oval, extended to posterior margin of sternum VIII ( Figure 14 View Figure 14 (c,d)). In the nymph: 1) lamellae of gill I moderately expanded forward and narrowed apically ( Figure 9 View Figure 9 (i)); 2) abdominal terga with paired small submedian spines and blunt denticle posteriorly ( Figure 9 View Figure 9 (h)).

The nymph of E. ( P.) falcatus sp. nov. is most similar to that of E. ( P.) bifurcatus . They both have paired small submedian spines and blunt denticles along posterior margin of abdominal terga. But E. ( P.) bifurcatus can be distinguished by the somewhat expanded gills I ( Figure 6 View Figure 6 (e)), which are moderately expanded in E. ( P.) falcatus sp. nov. In addition, the imaginal characters of E. ( P.) aculeatus are very similar to E. ( P.) falcatus sp. nov., especially the colouration pattern of abdomen (see Webb and McCafferty 2006a: Figures 1 View Figure 1 and 2 View Figure 2 ). However, the penis of E. ( P.) aculeatus differs from that of E. ( P.) falcatus sp. nov. by the absence of the lateral hooked projections and the smaller titillators ( Figure 13 View Figure 13 (f)).

As a new species belonging to the ‘paired-spines’ species in China, E. ( P.) falcatus sp. nov. possess similar imaginal characters as E. ( P.) aculeatus and its titillators on penes are distinct. Therefore, it is possible that all the male imagoes of ‘paired-spines’ species may have titillators.

Distribution

China ( Guizhou, Guangxi, Hunan) .