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

Ma, Zhen-Xing, Lei, Zhi-Ming, Li, Wen-Juan & Zhou, Chang-Fa, 2021, A revision of Epeorus (Proepeorus) in China, with descriptions of two new species (Ephemeroptera, Heptageniidae), Journal of Natural History 55 (17 - 18), pp. 1131-1159 : 1144-1152

publication ID	https://doi.org/ 10.1080/00222933.2021.1936679
persistent identifier	https://treatment.plazi.org/id/650487C7-FF94-FF9E-FE66-FF5CFDECFB21
treatment provided by	Plazi
scientific name	Epeorus (Proepeorus) falcatus
status	sp. nov.

Treatment

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) .