Epeorus (Belovius) khayengensis Boonsoong and Braasch

Braasch, Dietrich & Boonsoong, Boonsatien, 2010, A contribution to the Heptageniidae (Insecta, Ephemeroptera) of Thailand and Malaysia, Zootaxa 2610, pp. 1-26 : 13-17

Epeorus (Belovius) khayengensis Boonsoong and Braasch sp. nov.

Description. Mature La: Body length 10.5 mm; length of caudal filaments 11.5 mm. Body generally brown, with lighter and darker markings (Fig. 53).

Head: Length 1.3 mm, width 2.1 mm; brown, with conspicuous marks (Fig. 54); subquadrangular; anterior and lateral margins convex, with rows of dense hairlike setae; posterior margin slightly concave. Compound eyes black. Antennal scapes and pedicels brown, flagellae pale. Labrum (Fig. 55) with 3 large ridges on apical margin, with long hairlike setae on lateral margin, and with notch on anterior margin. Mandible (Figs. 56–57) with scattered setae along the molar area; incisor slightly developed. Maxillae (Fig. 58) each without armature on crown of galea-lacinia, apically with 3 acute teeth; medially with fine setae; terminal segment of maxillary palp with dense rows of hairlike setae. Hypopharynx (Fig. 59): Lingua with anterolateral lobes; superlinguae slightly expanded, laterally with rows of dense hairlike setae. Labium (Fig.

60) with broad V-shaped separation of glossae; glossae subtriangular; paraglossae slightly expanded laterally; apical segment of each palp acutely pointed, dorsal surface with dense row of comb setae.

Thorax: Pronotum with some dark marks (Fig. 53). Legs (Fig. 61) with 2 dark brown, median spots, lateral spots greyish, scattered short, ovate bristles on dorsal surfaces (Fig. 62), distally dark brown; tibiae basally brown, having long brown band in the middle, tarsi darkened, fringe of stout long hairs at posterior margins of femora, tibiae and tarsi. Length of femur 2.57, width 1.17 mm, length of tibia 2.34, width 0.18 mm, length of tarsus 0.59 mm; claws with 4–5 denticles (Fig. 63).

Abdomen: Abdominal terga brown, terga without spines, but with striking pattern (Fig. 65); hind margin of tergum provided with tooth-like bristles (Fig. 64); terga II–VII with long postero-lateral extensions (Fig. 65); sterna light yellowish without markings but partially visible muscle impressions. Lamellae of gill I somewhat extended beneath abdomen (Fig. 66). Gills II–VII with anal ribs arched and last rib straight (Figs. 67–68, see arrow); middle pairs large with wide rounded anal-proximal projections; gill faces with exception of marginal parts reddish tinged, scattered with very fine dotting; cerci with row of hairlike setae dorsally.

PLATE VIII. FIGURE 53. Habitus of Epeorus (Belovius) khayengensis sp. nov. 53, Dorsal habitus.

PLATE IX. FIGURES 54–60. Larva of Epeorus (Belovius) khayengensis sp. nov. 54, Head capsule. 55, Labrum, dorsal view (left) and ventral view (right). 56, Left mandible. 57, Right mandible. 58, Left maxilla, ventral view. 59, Hypopharynx, dorsal view (left) and ventral view (right). 60, Labium, dorsal view (left) and ventral view (right).

Etymology: This species is named for the stream, where the type material was collected: Khayeng stream, Thailand.

Diagnosis: Epeorus (Belovius) khayengensis sp. nov. is the only species of this subgenus from South-East Asia having no spines on its terga. It is easily separated from Epeorus (Belovius) carinatus Braasch & Soldán, 1984 , which has a row of submedian paired spines and from E. (B.) unicornutus , having a median row of single spines on the margins of the hind terga.

Discussion. Kluge (2004), understanding Belovius Tshernova, 1981 as a subgenus, transferred Epeorus carinatus from Vietnam to E. (Belovius) carinatus , characterized inter alia by anal ribs on gills II–VII. Originally, Tshernova (1981) published Belovius as a distinct genus, later documented by Hubbard (1990: p.7) in his ‘Mayflies of the World’ as “ Belovius Tshernova (As) ”. Webb and McCafferty (2008) did not recognize the subgenera of Epeorus (e.g. Belovius ) and other for seeing them as paraphyletic. In our opinion, we agree with a statement by Wang and McCafferty (2004: p. 27) in their ‘Phylogenetic Higher Classification’ on Heptageniidae : “As mentioned previously, the genus Epeorus does not appear to be divisible into additional cladistically sound species groups, each with exclusive synapomorphies. However, the group is in severe need of a global revision at the species level, which could possibly yield data revealing such additional groupings. Within the strict rules of phylogenetic classification ( Wiley 1981), additional genera would only be possible if they were sequentially derived with Epeorus …” So far as we know, that study has not occurred and therefore, provisionally, we hold on to the validity of subgenus Belovius within genus Epeorus , but also to genus Iron . We are convinced that all conclusions regarding this are arbitrarily at present.

PLATE X. FIGURES 61–68. Larva of Epeorus (Belovius) khayengensis sp. nov. 61, Foreleg, left, dorsal view. 62, Bristles at face of foreleg femur. 63, Foreleg, tarsal claw. 64, Abdominal tergum VII, posterior margin. 65, Abdominal terga I–X. 66, Gill I. 67, Gill V. 68, Gill VII.

Material examined: HOLOTYPE: mature male La, Thailand, Kanchanaburi Province, Thong Pha Phum district, Huai Khayeng streams, alt. 210 m, 14º35'07"N, 98º34.9'37"E; 13.XII.2008 (BB); PARATYPES: 9 La (3 mature), same data as above.

Types deposition: HOLOTYPE: mature male La ( ZMKU, 80 % alcohol); PARATYPES: 7 La ( ZMKU, 80 % alcohol); 1 male La, 1 female La (DBP).