Vietnamella maculosa, Auychinda & Sartori & Boonsoong, 2020

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

Vietnamella maculosa sp. nov. Figs 1A , 2A-G , 3A-L , 4A, D, G, J , 5A, B , 6A-C

Material examined.

Holotype: 1 male larva Thailand, Chiang Rai Province, Mueang Chiang Rai, Pong Phra Bat waterfall, 20°00'41.0"N, 99°48'15.0"E, 470 m, 6.V.2019, D. Chainthong leg. [ZMKU]. Paratypes: 2 larvae same data as holotype; 1 larva on slide [ZMKU] and another in ethanol [MZL GBIFCH00673059]. Both paratypes were used for DNA extraction.

Description.

Mature larva (in alcohol, Fig. 1A ). Body length 11.25 mm without cerci; cerci 4.8 mm; body brown with dark brown markings on thorax and femora.

Head. Brown with a pair of occipital tubercles, a single sub-occipital tubercle medially; two projections below eyes; inner pairs of projections small, spine-like and sharp (Fig. 2A ); outer pair large, triangular, cone shaped without any serrated spines (Fig. 4A, D ). Labrum, similar to other vietnamellid mayflies, anterior half of dorsal surface and margins with relatively long setae, ventral surface with short setae (Fig. 2B ). Labium, glossae width greater than length, glossae and paraglossae with dense setae on surface, setae on dorsal surface and margins longer; labial palpi three segmented, basal segment broader and longer than the second, apical segment very small; palpi with tiny setae (Fig. 2C ). Left mandible, slender, a little concave at sub-median area; molar block-like shape with a tuff of short setae below inner molar margin (Fig. 2D ). Right mandible, slender, slightly concave at sub-median area; molar block-like shape with a row of setae below inner molar margin (Fig. 2E ). Maxillae slender; maxillary palpi three segmented, with tiny setae; length ratio from basal to apical = 1.3:1.2:1 (Fig. 2F ). Hypopharynx, lingua square and superlinguae nearly round, with setae on surface (Fig. 2G )

Thorax. Pronotum with small moderately sharp anterolateral projections, and slightly pointed protuberances below the anterolateral projection (Fig. 3A ). Forefemur, strongly expanded with serrations or teeth projections on ventral margin (Fig. 3B ); transverse ridge serrated with small rounded setae (Fig. 5A, B ) and long thin setae near inner dorsal margin. Midfemur without any projection, expanded, dorsal margin convex apically and with a row of hair-like setae (Fig. 3C ). Hindfemur without any projection, expanded, longer than midfemur, dorsal margin with a row of hair-like setae (Fig. 3D ). All claws similar, strongly hooked with a single small denticle basally (Fig. 3E ).

Abdomen. Tergites I-X with a pair of median ridges or tubercles; posterolateral angles of tergites II-X extended into sharp projection; tergite VII with a pair of tubercles (Fig. 4G ) and tergite X with well-developed a pair of tubercles (Fig. 4J ); lateral margins of tergite with dense setae. Gill on segments I-VII: gill I finger-like with setae (Fig. 3F ); gills on segments II-VI similar in structure, with dorsal and ventral lamellae, the latter further divided into two clusters, each with several smaller lobes (Fig. 3G-K ); gill on segment VII small, with two lamellae but ventral lamella divided into three lobes (Fig. 3L ). Caudal filaments with dense lateral setae on inner and outer margins of middle part.

Eggs. (dissected from mature larva). Length 200 µm, width 144 µm; oval shape, chorionic surface with small protuberances, half of egg covered with helmet-shaped polar cap (Fig. 6A ); rod shaped KCT (Knob Terminated Coiled Thread) around egg body (Fig. 6B ); 2 or 3 tagenoform-type micropyles at centre (Fig. 6C ).

Diagnosis.

The larva of Vietnamella maculosa sp. nov. is most similar to that of V. thani and V. sinensis in the lack of serrations on the outer projection on the head, but it can be separated from V. thani based on the following characteristics: i) the pattern of serration on the ventral margin of the forefemur, ii) the setae on the transverse ridge of the forefemur, iii) a well-developed pair of median ridge projections of tergite X. It can be separated from V. sinensis by the proportion of the maxillary palp on the second segment, which is slightly longer than on the third segment (1.2:1), whereas in V. sinensis it is clearly longer (1.6:1).

Remarks.

The larvae of Vietnamella maculosa sp. nov. have a unique colour pattern, with brown and dark brown banding spread over the body and femurs. However, this colour can change in intensity depending on the life stage and environment. Other species, like V. thani , have variation in body colour but do not have this pattern.

Etymology.

The name maculosa (Latin for having spot or macula), refers to the brown and dark brown banding of the species.

Distribution.

Chiang Rai Province

Adult.

Unknown

Figures

Figure 1. Vietnamella spp. A Vietnamella maculosa sp. nov., habitus in dorsal view B Vietnamella sp. B, habitus in dorsal view. Scale bars: 1 mm.

Figure 2. Vietnamella maculosa sp. nov. A ventral view of head with outer projection and small inner projection (arrow) B labrum C labium D left mandible E right mandible F maxilla G hypopharynx. Scale bars: 1 mm (A); 0.1 mm (B-G).

Figure 3. Vietnamella maculosa sp. nov. A thorax B forefemur C middle femur D hind femur E foreleg claw F first gills on segment I (arrow) G gill II H gill III I gill IV J gill V K gill V L gill VII. Scale bars: 1 mm (A-D, F); 0.2 mm (G-L); 0.1 mm (E).

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 6. SEM of egg structure of Vietnamella maculosa sp. nov. A overview B detail of Knob Terminated Coiled Thread (KCT) C micropyle and chorionic surface. Scale bars: 50 µm (A); 20 µm (B); 10 µm (C).