Vietnamella thani Tshernova, 1972

Auychinda, Chonlakran, Sartori, Michel & Boonsoong, Boonsatien, 2020, Vietnamellidae (Insecta, Ephemeroptera) of Thailand, ZooKeys 902, pp. 17-36 : 17

Vietnamella thani Tshernova, 1972 Figs 4C, F, I, L , 5C , 7A-O , 8A-O , 9A-N , 10B, C , 11A-C

Vietnamella thani Tshernova, 1972: 604-614, fig. 4 (orig.); Hu et al. 2017: 381-390, fig. 7 (distribution).

Material examined.

Thailand; Kanchanaburi Province, Thong Pha Phum, Huai Pak Kok, 14°35'01.4"N, 98°34'54.0"E, 161 m, 15.X.2015, 1 larva; 20.II.2016, 1 larva; 21.II.2016, 3 larvae, 1 female imago; 31.I.2019, 9 larvae, 1 male subimago (reared), 1 male imago (reared). Huai Khayeng, Ban Prachum Mai, 14°39'34.0"N, 98°32'02.0"E, 233 m, 20.II.2016, 4 larvae, [ZMKU]; 13.XII.2014, 1 larva, all B. Boonsoong leg; 15.X.2015, 3 larvae, B. Boonsoong & M. Sartori leg. [MZL]. Prachuap Khiri Khan Province, Kui Buri, Huai Samrong, 12°03'55.0"N, 99°37'38.0"E, 103 m, 11 larvae, D. Chainthong leg. [ZMKU].

Diagnosis.

The larva of Vietnamella thani can be distinguished from those of other Vietnamella based on the following characteristics: i) outer pairs of projections on the head are long, triangular, and cone shaped without serrated spines; ii) the first and second segments of the maxillary palpi have an equal length ratio; iii) the forefemur has a serrated transverse ridge with spatulate setae (Fig. 5C ); and iv) the abdominal tergite X either lacks or has a poorly-developed pair of tubercles (Fig. 4L ).

Description of imagoes.

Male imago (in alcohol, Figs 7 , 10C ). Head. Eyes rounded with ventral part brown-yellowish and dorsal part yellowish (Fig. 7A, B ). Thorax. Forelegs (8.07 mm), length ratio of femur and tibia = 1:1.45; length ratio of four tarsal segments is 3:2:1.5:1 (Fig. 7C ). Midlegs (4.76 mm), length ratio of femur and tibia = 1.2:1; length ratio of four tarsal segments is 1:1:1:3 (Fig. 7D ). Hindlegs (4.97 mm), length ratio of femur and tibia = 1.4:1; length ratio of four tarsal segments is 1:1:1:4 (Fig. 7E ). Mesonotum with a notable median longitudinal suture, two medioparapsidal sutures (Fig. 7F ). Mesosternum with a square basisternum, broad furcasternum (Fig. 7G ). Forewings, numerous crossviens. MA forked middle of wing, MP forked basally, three intercalaries between MP1 and MP2; CuA and CuP adjacent at base; cubital field with three bifurcate veins arising from CuA (Fig. 7H ). Hind wings rounded, leading margin slightly concave, with clear crossveins; seven crossveins with one bifurcate between Sc and RA; three crossveins between MA and MP (Fig. 7I ). Abdomen. Genitalia with three-segmented forceps (1.2 mm), first segment = 0.6 mm, second segment = 0.45 mm, apical segment = 0.15, small and nearly rounded; penes (0.76 mm) totally fused with a shallow median cleft; subgenital plate slightly convex (Fig. 7J-L ). Abdominal segment IX with lateral projection, white stripe on sternites VII-IX (Fig. 7M-O ).

Male subimago. (in alcohol, Fig. 8 ). Head. Eyes rounded; dorsal part dark grey; ventral part brown (Fig. 8A, B ). Thorax. Forelegs (6.38 mm), length ratio of femur and tibia = 1:1.1; length ratio of four tarsal segments is 1.6:1:1:1.3 (Fig. 8C ). Midlegs (5.41 mm), length ratio of femur and tibia = 1.4:1; length ratio of four tarsal segments is 1.3:1:1.1:3.4 (Fig. 8D ). Hindlegs (5.58 mm), length ratio of femur and tibia = 1.6:1; length ratio of four tarsal segments is 1.4:1:1.2:3.4 (Fig. 8E ). Mesonotum, brown with a notable median longitudinal suture (Fig. 8F ). Mesosternum, pale red with a square basisternum, broad furcasternum (Fig. 8G ). Forewing and hindwing are similar to imago but more opaque and having more visible crossveins (Fig. 8H, I ). Abdomen. Genitalia similar to those of imago but forceps and penes shorter and broader; forceps with total length = 1.0 mm, first segment = 0.53 mm, second segment= 0.40 mm and third segment = 0.07 mm; penes length = 0.7 mm (Fig. 8J-L ). Abdomen brown and pale red dorsally, segment IX with notable lateral projections (Fig. 8M-O ).

Female imago. (in alcohol, Fig. 9 ). Head. Eyes rounded, dark brown without dorsal eyes (Fig. 9A, B ). Thorax. Forelegs (7.2 mm), length ratio of femur and tibia = 1.4:1; length ratio of four tarsal segments is 1:1:1:3.7 (Fig. 9C ). Midlegs (6.4 mm), length ratio of femur and tibia = 1.2:1; length ratio of four tarsal segments is 1:1:1.2:2.8 (Fig. 9D ). Hindlegs (7.2 mm), length ratio of femur and tibia = 1:1, length ratio of four tarsal segments is 1:1.2:1.1:2.6 (Fig. 9E ). Mesonotum brown with a notable median longitudinal suture (Fig. 9F ). Mesoternum pale red with rectangle basisternum, broad furcasternum (Fig. 9G ). Forewing, 14 crossveins in stigmatic area; MA forked middle of wing; MP forked basally, 3 intercalaries between MP1 and MP2; CuA and CuP adjacent at base (Fig. 9H ). Hindwing rounded, leading margin slightly concave, with clear crossveins, 7 crossveins between MA and MP (Fig. 9I ). Abdomen. Tergites brown, sternites pale red, sternites VIII-IX brown (Fig. 9K-N ). Subanal plate brown with shallow median cleft (Fig. 9J ). Subgenital plate weakly developed, pale, with shallow median emargination (Fig. 9N )

Eggs. (dissected from female imago). Length 175 µm, width 125 µm; oval shape, chorionic surface with small protuberances, half of egg covered with helmet-shaped polar cap (Fig. 11A ); many KCT around egg body (Fig. 11B ); 1 or 2 tagenoform-type of micropyles at centre (Fig. 11C ).

Distribution.

Kanchanaburi and Prachuap Khiri Khan Provinces, Thailand.

Remarks.

The larvae of Vietnamella thani are widely distributed in Thailand. They inhabit fast-flowing streams (Fig. 10A ) but have never been reported in southern Thailand. Vietnamella thani have notable outer pairs of projections on head without serrated spines that differ from Vietnamella sp. B. The larvae show colour variations and can be greenish, yellow or brown. The imaginal stages of V. thani have similar characters to those of V. sinensis but lack the longitudinal vein on the stigmatic area of the forewing and they have less crossveins between Sc and RA on the hindwings (Table 4 ). The egg structure is covered by a membrane, which leads to unclear sculpturing of the surface, especially in the posterior part of the egg. Thus, the egg from this study showed little difference from the egg structure of V. sinensis .

Figures

Figure 4. Vietnamella spp. Vietnamella maculosa sp. nov. (A, D, G, J): A outer projection on head (arrow) D inner and outer projections on head G, J tubercle on tergite VII and X; Vietnamella sp. B (B, E, H, K): B outer projection on head (arrow) E inner and outer projections with serration on head H, K tubercles on tergite VII and X; Vietnamella thani (C, F, I, L): C outer projection on head (arrow) F inner and outer projections on head I, L tubercles on tergite VII and X. Scale bars: 1 mm (A-C); 0.5 mm (G); 0.1 mm (D-F, H, I); 0.05 mm (J-L).

Figure 5. Forefemur and setae A forefemur of Vietnamella maculosa sp. nov. with serration of transverse ridge (arrow) B setae on transverse ridge of Vietnamella maculosa sp. nov. C setae on transverse ridge of V. thani. Scale bars: 1 mm (A); 0.01 mm (B, C).

Figure 7. Male imago of Vietnamella thani A dorsal view of head B lateral view of head C foreleg D middle leg E hindleg F, G dorsal and ventral view of thorax H forewing I hindwing J ventral view of genitalia K dorsal view of genitalia L lateral view of genitalia M dorsal view of abdomen N lateral view of abdomen O ventral view of abdomen. Scale bars: 1 mm.

Figure 8. Male subimago of Vietnamella thani A dorsal view of head B lateral view of head C foreleg D middle leg E hindleg F, G dorsal and ventral view of thorax H forewing I hindwing J ventral view of genitalia K dorsal view of genitalia L lateral view of genitalia M dorsal view of abdomen N lateral view of abdomen O ventral view of abdomen. Scale bars: 1 mm.

Figure 9. Female imago of Vietnamella thani A dorsal view of head B lateral view of head C foreleg D middle leg E hindleg F, G dorsal and ventral view of thorax H forewing I hindwing J, K ventral and dorsal view of genitalia L dorsal view of abdomen M lateral view of abdomen N ventral view of abdomen. Scale bars: 1 mm.

Figure 10. Vietnamella thani A habitat B habitus of larva C habitus of male imago (incomplete molting).

Figure 11. SEM of egg structure of Vietnamella thani A overview B detail of Knob Terminated Coiled Thread (KCT) and chorionic surface C micropyle. Scale bars: 50 µm.