Rhithrogena (Tumungula) siamensis, Braasch, Dietrich & Boonsoong, Boonsatien, 2009

Braasch, Dietrich & Boonsoong, Boonsatien, 2009, A new Notacanthurus Tshernova, 1974 and a new Rhithrogena Eaton, 1881 (subgenus Tumungula Zhou & Peters, 2004) from Thailand (Heptageniidae, Ephemeroptera), Zootaxa 2166, pp. 33-44 : 38-43

Rhithrogena (Tumungula) siamensis sp. n.

Description. Male: Body length 7.4 mm; length of forewing 7.4 mm, length of caudal filaments 12.7 mm.

Head (Fig. 19): Compound eyes nearly contiguous, grey blue, at base darker blue. Prothorax: Dorsally beige, flanked by tan stripes on both sides. Legs: Forefemur reddish brown with longish jet-black spot, tibia tan, proximally and distally darkened, last segment of tarsus darkened; middle and hind legs light with longish jet-black femur spot (Figs. 22 – 24). Proportions of forefemur: tibia: tarsus (tarsal segments) in mm are 1.76: 2.3: 3.2 (1.1: 0.77: 0.62: 0.48: 0.22); hind legs 1.98: 1.5: 0.47 (0.13: 0.06: 0.04: 0.04: 020). Anterotarsal claw with blunt portion remarkably enlarged to a brown sclerotized, somewhat heart-shaped capsula that includes a balloon-shaped pulvillus (Fig. 25) protruding from the apical margin of the capsula; pointed portion of claw broad-based, shorter, with curved tapering tip; at middle and hind legs blunt portion of claw more elongated, pad-like, apically obliquely rounded (Figs. 26 – 27). Wings: Wings transparent, longitudinal veins weakly yellowish, pterostigma whitish (Fig. 20). Venation of hind wing as shown in Fig. 21.

Abdomen: Terga with blackish pattern (Fig. 28); sterna whitish. Genitals. Genital segment (Fig. 29) of male with long forcipes, styliger plate convex, medially pointed, its flanks with strongly elevated and tapered projections, slightly bent inwards; penis (Fig. 30) widely opened with divergent lobes without apical hooks around gonopore and lacking titillators. Cerci: In proximal third brownish, distally lightened, faintly darkened at joints.

Description Female: Size: Body length 6.9 mm, length of forewing 7.0 mm, length of caudal filaments 9.9 mm.

Head: Compound eyes blue grey, separated by a distance of 4.2x width of median ocellus; vertex between eyes and ocelli tan with pattern of brownish spots.

Prothorax: Upper parts of prothorax principally very similar to that of male. Legs: Legs of same colour as in male; proportions of femur: tibia: tarsus (tarsal segments) of foreleg in mm 1.65: 2.2: 1.25 (0.22: 0.22: 0.13: 0.11: 0.26) and hind leg with 1.65: 1.65: 0.53 (0.08: 0.09: 0.07: 0.12:0.17). Wings transparent with weakly expressed longitudinal veins and whitish pterostigma.

Abdomen: Dorsal segments very similar to that of male, but with slight reddish tinge; sterna of light colour except sternum VI having two parallel, elongated smudges. Subanal plate by half of sternum length acutely cleft (Fig. 31). Cerci: Cerci marked as in male.

PLATE IV. FIGURE 19–31. Imagines of Rhithrogena (Tumungula) siamensis sp. n. 19, Male head, dorsal view. 20, Male forewing, dorsal view (right). 21, Male hindwing, dorsal view (right). 22, Male foreleg, posterior view (right). 23, Male middle leg, posterior view (right). 24, Male hindleg, posterior view (right). 25, Male foreclaw, dorsal view (right) and ventral view (left). 26, Male, claw of middle leg, dorsal view (right). 27, Male, claw of hindleg, dorsal view (right). 28, Male, abdominal tergum, color pattern. 29, Male genitalia, ventral view. 30, Penis, dorsal view (left) and ventral view (right). 31, Female, terminal sterna, ventral view.

Description:? Larva, male (unreared): Body length 6.0 mm; length of cerci 7.0 mm.

Head: Head (Fig. 32) brown, sides darkened, medially with conspicuous dark spot above median ocellus and dark spot at median suture base above hind margin;.anterior margin evenly rounded; antennae 3/ 4 x width of head. Labrum (Fig. 33) 0.3 x width of head capsule, with shallow median notch, short hairs scattered on anterior margin. Mandibles (Figs. 34 – 36): outer incisor longer than inner incisor, margin serrated (Fig. 35); prostheca represented by approximately 8 finely branched setae (Fig. 36). Maxillae (Fig. 37): galea-lacinia consisting of nine stout, pectinate, comb-like setae, basal segment expanded basally, apical segment pointed, covered ventrally with small, pectinate setae (Fig. 38). Hypopharynx with lingua truncate at apex (Fig. 39). Labium with broad V-shaped separation between glossae, paraglossae moderately expanded laterally (Fig. 40).

PLATE V. FIGURE 32. Larva of Rhithrogena (Tumungula) siamensis sp. 32, Dorsal habitus

Thorax:. Colour brown. Legs: Femora of all legs pale and with median dark marking (Fig. 41), regular row of setae on outer margin; dorsal surface with spatulate setae (Fig. 42). Claws of legs with 4 subapical denticles (Fig. 43).

Abdomen: Abdominal segments brown, terga V-VII with pair of submedian smudges, last three paler (Fig. 32). Sterna pale, sternum IX notched (Fig. 44). Gills on abdominal segments I – VII; gill I large, with smooth margins and few pointed crenulations, plica long, narrowly rounded (Fig. 45); gills II – VI with oval lamellae (Fig. 46); gill VII with smooth margins (Fig. 47); all gills with well-developed tufted tracheal tubes. Three caudal filaments with whorls of minute spines at articulations.

Subimagines. Unknown.

PLATE VI. FIGURE 33–40. Larva of Rhithrogena (Tumungula) siamensis sp. n. 33, Labrum, dorsal view (left) and ventral view (right). 34, Right mandible, ventral view. 35, Right mandible, dorsal detail of incisors. 36, Left mandible, ventral view. 37, Left maxilla, ventral view. 38, Maxillary palp, detail of setae. 39, Hypopharynx, dorsal view (left) and ventral view (right). 40, Labium, dorsal view (left) and ventral view (right).

Larvae. Unreared, not known for sure.

Etymology: Species name refers to region of first discovery: Siam, former Kingdom of Thailand.

Diagnosis: The male of the new species resembles that of R. (Tumungula) unica Zhou & Peters, 2004 with hypertrophied foretarsal claw, basal tarsal segment roughly 1.4x longer than second, deeply excavated genital segment, styliger exhibiting remarkable projections and penis without titillators. In contrast to R. (T.) unica , the blunt part in the middle and hind claw is conspicuously longer than that in R. (T.) unica ; the extended styliger projections of R. (T.) siamensis are not straight, but directed inwards, while the penis lobes are more elongated, being apically without reversed hook but having round gonopores. In presumed larva, differences are seen in mouthparts: labrum at outer rim without distinct medial emargination and dentate corners as in R. (T.) unica ( Zhou & Peters 2004, p. 900, fig. 16); glossae are placed more distantly, leaning in laterad position; mandibles with outer incisor somewhat longer and narrower than in R. (T.) unica , inner incisor apically pointed; gill I differs in being pointed-crenulate and having longer plica more flatly rounded, whereas that of R. (T.) unica has a few unpointed crenulations and a shorter, more strongly rounded plica. The Sumatran species R. diehliana Braasch & Soldán, 1986 b, a male subimago, very much resembles that of R. (T.) unica b y Zhou and Peters (2004: M: p. 899, fig. 3) in having exorbitant extensions of styliger, but gonopores each having somewhat bean-shaped outlines with concave sides directed inwards. Unfortunately, the legs are lost and so there is no certainty in comparison. However, its penis lobes differ from those of R. (T.) unica by the gonopores having a much wider opening and lacking a reversed hook.

PLATE VII. FIGURE 41–47. Larva of Rhithrogena (Tumungula) siamensis sp. n. 41, Right foreleg, dorsal view. 42, Foreleg, setae on middle section of anterior face, dorsal view. 43, Foreleg, tarsal claw. 44, Abdominal sterna, posterior end. 45, Gill I, ventral view (right). 46, Gill IV, ventral view (right). 47, Gill VII, ventral view (right).

Discussion: The genus Rhithrogena seems to be underrepresented in Southeast Asia: Rhithrogena spp. was not present in the samples of the Gombak study in Malaysia by Braasch and Soldán (1986a) nor in the collections of I. Sivec ( Slovenija) at Belum River, Hulu Perak in Malaysia in the early 1990s. No Rhithrogena specimens were obtained in collections from Vietnamese rivers by T. Soldán in the 1980s. In field collections by Sites et al. (2001) in the 10 southern provinces of the Thai peninsula, no species of the genus was recorded. However, one unnamed species was found in the extensive benthos inventory in northeastern Thailand by Sangpradub et al. (2002), possibly the same as in the western part of North Thailand. Thus, the apparently disjunctive existence of the genus on Java, Sumatra and the Lesser Sunda Islands ( Braasch 2005; Braasch & Soldán 1986; Edmunds & Polhemus 1990; Ulmer 1939) is surprising from a zoogeographic point of view and still demands further explanation. For example, R. diehliana (Braasch & Soldán 1986: subimago male, p. 92: Fig. 1–2) from Sumatra could belong to subgenus Tumungula as evidenced by the long styliger projections in its species. Further, it might be suggested that R. parva (Ulmer 1912: larva, p. 374: Fig. 8–10) from Java could be closely related to above-mentioned R. diehliana .

Biology: In northern Thailand, flight of R. siamensis was very intensive in the morning and after dusk, giving the impression of considerable movement of Rhithrogena along river banks. So far, subimagines have not been found at places with abundant imaginal presence, merely one larva could be recorded. Otherwise, collections over most of the year revealed that the flight season at altitudes of> 600 m was mainly in March/ April, just before the beginning of monsoon rains in May. Only a few dates are out of this time, possibly due to different altitude (Mae Kaem) or low temperature conditions (small affluent). More speculative would be the assumption that in October, at the beginning of the dry season, a first, smaller generation could fly. However, there are few mayfly collections in the months between October and January.

Material examined: HOLOTYPE: Male, THAILAND, North, Mae Hong Son Province, Soppong/ Pangmapa, Nam Lang River, 19°34.447’N, 98° 18.727 E, altitude 605 m, 03-27.IV-03, at light, DB, in 70% alcohol. PARATYPES: 52 males, 15 females, North Thailand, Mae Hong Son Province, Soppong/Pangmapa, Nam Lang River 19°34.447’N, 98° 18.727 E, altitude 605 m, 03-27.IV-03, at light, DB, in 70% alcohol; 1 male, 2 females, same locality, 03-II-05-III-04, at light, DB; 2 females, same locality, 28-X-04, at light, DK; 4 males, same locality, 12-III-07, DK; 23 males, same locality, 30-III-07, at light, DK; all samples in 70% alcohol;. 2 males, 1 female, North Thailand, Mae Hong Son Province, Soppong/ Pangmapa, small affluent stream, 19°31’01.72”N, 98°14’53.79’’E, altitude 605 m, 12-VI-05, at light, DK.

Further material: 2 females, North Thailand, Chiang Mai Province, Mae Chaem River, 10 km above Hot, 18°12’07.54’’N, 98°36’32.85’’E, altitude 268 m, 01-III-04;.at light, DB; 1 female, North Thailand, Mae Kae Waterfall, near Pai, 19°15’01.42’’N, 98°38’19.17’’E, altitude 1690 m, 23-II-07, at vegetation, DB.

Larval material of Rhithrogena sp.? from 4 geographically different localities in North Thailand, apparently of one species; however, affiliation to R. (Tumungula) siamensis needs confirmation by rearing.

1 larva, North Thailand, Chiangmai Province, Soppong/Pangmapa, Nam Lang River, 19°31’01.72’’N, 98°14’53.79’’E, altitude 605 m, 10-III-08; 2 larvae, North Thailand, Chiang Mai Province, Doi Inthanon National Park, river below Headquarters, 18°31’33.35’’N, 98°29’57.20’’E, altitude 1690 m, 20-II-04; 1 larva, North Thailand, Chiang Mai Province, Mae Chaem River, above Hot Resort, 18°07N, 98°32’E, altitude 200 m, 01-III-04, DB; 3 larvae, North Thailand, Chiang Rai Province, above Thaton, Kok River, 20°03’39.10’’N, 99°21’43.94’’E, altitude 844 m, 01-III-04; all bottom samples, DB.

Types deposition: HOLOTYPE: male [ MNHU], PARATYPES: males, females for a time in DBP; 2 males, 2 females in SMF Eph; 2 males, 1 female in ZMKU.