Megabranchiella longusa Phlai-ngam & Tungpairojwong, 2022

Phlai-ngam, Sirikamon, Boonsoong, Boonsatien, Gattolliat, Jean-Luc & Tungpairojwong, Nisarat, 2022, Megabranchiella gen. nov., a new mayfly genus (Ephemeroptera, Baetidae) from Thailand with description of two new species, ZooKeys 1125, pp. 1-31 : 1

Megabranchiella longusa Phlai-ngam & Tungpairojwong sp. nov.

Holotype.

One male larva on slide and SEM stubs (KKU-AIC), Thailand, Chiang Mai, Chom Thong district, Ban Luang, Siribhum waterfall, 18°32'50.02N, 98°30'49.79E, 1,359 m, 11.03.2021, B. Boonsoong and C. Sutthinun leg.

Paratype.

One larva in alcohol (ZMKU), same data as holotype.

Other materials.

One larva in alcohol (MZL), Thailand, Nan, Bo Kluea district, Kluea district Tai , Sapan River , 19°09'19.09N, 101°10'12.96E, 995 m, B. Boonsoong and C. Suttinun leg.

Description.

Coloration (Fig. 9A-B ). Head dorsally brownish, darker brown along frontal suture. Thorax dorsally brown; pronotum with dark brown pattern medially, mesonotum with longitudinally darker brown pattern medially. Abdomen light brown with dark brown pattern; tergites I-VIII brownish, with darker brown marks laterally to posterior margin, tergites II-III with a paired of pale dots medially, tergites IV-VIII with distinct paired of pale, oblique streak, and with a pale, longitudinal pattern medially, tergites IX-X paler than other tergites, with the same pattern as tergites IV-VIII; abdomen ventrally light brown (Fig. 9C ). Legs light brown; dorsal, ventral, and apical femur margins dark brown; claws distally dark brown. Caudal filaments brownish.

Body (Fig. 9 ). Ventrally flattened (Fig. 9C ), body length 3.5 mm, covered with scattered long, hair-like setae.

Head (Fig. 9B ). Lateral view rounded, head width ca. 1.2 × as long as head length.

Antenna. Ca. 2 × as long as head length (Fig. 9B ); scape without process, subequal in width and length, slightly shorter than pedicel, pedicel ca. 2 × as long as width, scape and pedicel almost bare, without scales bases, covered with scattered long, fine setae; flagellum covered with scattered long, fine setae.

Labrum (Fig. 10A ). Broadly rounded; wider than long, width ca. 1.17 × as long as length; dorsal surface with submarginal row composed of one long, point, simple seta medially plus three long, point, simple setae anterolaterally, dorsal surface with scattered simple, hairlike setae; distal margin with anteromedian notch shallow. Ventrally with submarginal row of setae composed of lateral and anterolateral long, feathered setae and medial long, pectinate setae; ventral surface with five short, spine-like setae near lateral and anterolateral margin.

Right mandible (Fig. 10B ). Canine (Fig. 10C ) with 4 + 4 apically rounded denticles, largely fused outer and inner incisors; inner margin of inner incisor with small denticulation; prostheca robust (Fig. 10D ), apically with small denticles and comb-shaped structure; mola between mola and prostheca smooth, without setae; mola with well-developed denticulation; apex of mola with tuft of spines like setae.

Left mandible (Fig. 10E ). Canine (Fig. 10F ) with 4 + 4 apically rounded denticles, largely fused outer and inner incisors; inner margin of inner incisor with small denticulation; prostheca robust, apically with small denticles and comb-shaped structure (Fig. 10G ); mola between mola and prostheca smooth, without setae; mola with reduced denticulation, molar area with numerous small, round teeth, apex of mola with tuft of spines like setae.

Maxilla (Fig. 10H ). Short and compact; galea-lacinia (Fig. 10I ) with long, robust, simple setae under crown; inner dorsal row of setae with denti-setae; distal denti-seta tooth-like, middle denti-seta (Fig. 10J ) slender, bifid and pectinate; proximal denti-seta slender, pectinate; inner ventral row of six robust, simple setae; medially with one seta and four simple setae. Maxillary palp 2-segmented, with scattered small, blunt setae; distal segment with distinct, small tip at apex.

Labium (Fig. 10K ). Short and compact; glossa basally broad, narrower toward apex, slightly shorter than paraglossa; inner margin with medium, pointed, simple setae; apex with four long, robust, pectinate setae. Paraglossa sub-rectangular, broader than glossa, apically curved inward, apical margin with three rows of long, robust, apically pectinate setae (Fig. 10L ), ventrally with 2-3 long, spine-like setae near inner margin, with an arch of 4-5 long, simple setae on outer margin. Labial palp 3-segmented, segment I rectangular and broad, covered with scattered fine, setae and several micropores; segment II with small distolateral expansion, with a few scattered, simple setae and a row of setae reduced to two large, blunt, robust, simple setae near distal margin; segment III rounded, covered with long, robust, simple setae.

Hypopharynx (Fig. 10M ). Lingua subequal to superlingua, apically rounded, with apical tuft of fine, short simple setae; superlingua with distal margin rounded, with fine, short simple setae along margin.

Thorax. Hindwing pads (Fig. 13A ). Highly reduced.

Forelegs (Fig. 12A ). Ratio of foreleg segments 0.68: 0.59: 0.25. Femur (Fig. 13B ). Length ca. 3 × maximum width. Dorsal margin of femur (Figs 11A , 13C-D ) with a row of 18-20 long, robust, apically pointed, laterally pectinated setae; short stout, lanceolate, laterally pectinate setae and scattered fine hair-like setae along dorsal and ventral margins; femora patch present; surface with scattered tiny spines anteromedially (Fig. 13E ); dense long, fine, small apically blunt, hair-like setae present; dorsal margin of tibia with a row of long, apically pointed, pectinate setae; several short stout, lanceolate, laterally pectinate setae and scattered short, apically pointed, hair-like setae along dorsal and ventral margins, patella-tibial suture present; tarsus dorsally with a row of fine, simple setae; ventral margin with a row of fine, simple setae; surface covered with scattered fine hair-like setae. Tarsal claw (Fig. 12B ) with one row of about 16 denticles increasing in length toward apex, subapical setae absent. Midlegs and hindlegs. As forelegs.

Abdomen (Fig. 11B ). Tergites. Posterior margin smooth, posterior marginal spines extremely reduced to absent (Figs 11C , 12C , 13F ), tergal surface with scattered fine, hair-like setae and scattered long translucent scales distally; abdominal sternites without posterior marginal spines, sternal surface with loose scattered, fine, hair-like setae.

Gills (Fig. 12D ). Seven pairs of gills present on abdominal tergites I-VII, slender and elongated; gills I (Fig. 11D ) enlarged to covered abdominal sternites II-V, oriented ventrally, relatively elongated shape with length approximately 2.5 × of width, medially part broad, tracheation extending from main trunk and outer margin, gill margin smooth, surface and gill margin without long, fine hair-like setae; gills II-VII oriented dorsolaterally, slightly oval and slender with length approximately 3.3 × of width, gill margin smooth, surface and gill margin covered with scattered long, fine hair-like setae.

Gonostyli bud (Fig. 11E ). Acentrella -type, three-segmented, segment I very short, 0.3 × of segment II length, segment III relatively short and broad, rounded at apex.

Paraproct (Fig. 12E ). Margin smooth without marginal spines and without prolongation at posterior margin, surface without scale bases, with micropores and fine, stout, simple setae and scattered fine, hair-like setae, and with a patch of notch scales.

Caudal filaments. Cerci 0.4 × of body length, inner margin of cerci with very thin, long setae; median filament 0.5 × of cerci length, lateral margins with very thin, long setae.

Winged stage.

Unknown.

Etymology.

The name of the species “longusa” refers to the outline of abdominal gill I which is elongate- shaped.

Distribution.

Northern part of Thailand (Chiang Mai and Nan Provinces) (Fig. 15 ).

Ecological notes.

The larvae were collected in Siribhum waterfall (Fig. 14D ) and headwater stream (Sapan River River) (Fig. 14E ). The sampling sites were located at high altitudes of 995-1,360 m a.s.l. in forest areas on mountains in the northern part of Thailand. The waterfall was in the upper stream of the Ping River, and the substrate types were dominated by boulders, cobbles, pebbles, gravel, and a sand bottom. The stream was in the Sapan River and located near the resort which can be disturbed by touristic attractions. The larvae were found on the surface and underside of cobbles in fast-flowing water (Fig. 14F ).

Figures

Figure 9. Megabranchiella longusa sp. nov., larval habitus: A dorsal view B lateral view C ventral view. Scale bars: 1 mm.

Figure 10. Megabranchiella longusa sp. nov., larval morphology A labrum B right mandible C right incisor D right prostheca E left mandible F left incisor G left prostheca H maxilla I apex of galea-lacinia J denti-seta K labium L long, robust, pectinate setae M hypopharynx.

Figure 11. Megabranchiella longusa sp. nov., larval morphology A dorsal margin of femur B dorsal view of abdomen C enlargement of abdominal tergites IV-VII D ventral view of abdominal gills I (arrow) E ventral view of gonostyli. Scale bars: 0.1 mm (A); 0.8 mm (B); 0.2 mm (C); 0.4 mm (D); 0.3 mm (E).

Figure 12. Megabranchiella longusa sp. nov., larval morphology A foreleg B tarsal claw C tergite V D abdominal gills I-VII E paraproct and notched scales on surface.

Figure 13. Megabranchiella longusa sp. nov., larval morphology (SEM) A hindwing pad B forefemur (dorsal view) C-D setae on dorsal margin of forefemur E spines on dorsal surface of forefemur F tergite V. Scale bars: 100 um (A, D, F); 400 um (B); 200 um (C); 30 um (E).

Figure 14. Type locality and larval habitats of Megabranchiella gen. nov. A-C type locality and larval habitats of M. scutulata sp. nov. A Mae Kampong stream, The Royal Project of Teen Tok, Chiang Mai Province B Pong Phra Baht Waterfall, Chiang Rai Province C fast-flowing water with pebble and cobble habitats (D-F) type locality and larval habitats of M. longusa sp. nov. D Siribhum waterfall, Chiang Mai Province E Sapan River, Bor Kluea district, Nan Province F fast-flowing water with boulder, cobble, and pebble habitats.

Figure 15. Distribution of genus Megabranchiella gen. nov. in Thailand A distribution of M. scutulata sp. nov. (red triangle) B distribution of M. longusa sp. nov. (blue triangle).