Microgomphus thailandica Asahina, 1981

Boonsoong, Boonsatien & Chainthong, Damrong, 2014, Description of the last stadium larva and female of Microgomphus thailandica Asahina, 1981 (Odonata: Gomphidae), Zootaxa 3811 (2), pp. 271-279 : 272-276

Microgomphus thailandica Asahina, 1981

( Figures 1–20)

Material examined: 3 last stadium larvae, 30.III.2013, Borwee waterfall (13°28.6’N, 99°14.5’E), Suanpung district, Ratchaburi province, Thailand, D. Chainthong leg.; 2 females and their exuviae, emerged on 24.IV.2013; 1 male, emerged 26.IV.2013.

Male adult. The key characters (head, pterothoracic pattern and caudal appendages) of male M. thailandica are shown in Fig. 2 , 4–7 .

Description of the female adult. General appearance and color pattern as shown in Fig. 3 .

Measurements (mm): Fw length 27.09; Hw length 25.38; abdomen with appendages 27.13.

Head: Head mainly black with parts yellow, with remarkable paired spines on posterior margin of occiput ( Fig. 8 ), postclypeus black, anteclypeus pale brown with median yellow spot, top of frons with two yellow spots, the spots are trapezoid, each separated by narrow stripe, labrum with two lateral yellow spots, mandible and labium almost brownish.

Thorax: Color pattern as shown in Fig. 9 . Prothorax black with yellow markings. Synthorax black with yellow markings. Dorsal view of synthorax with axe-shaped yellow stripes and yellow spots, each separated; each side of synthorax with alternation of two straight yellow and brownish stripes. Wings hyaline; pterostigma yellow, covering 4–5 cells; antenodals 15 in Fw, 10 in Hw, postnodals 11 in Fw, 10 in Hw; arc opposite second antenodal; 9 cross veins between sectors of arc from arc to bifurcation of Rs in Fw, 6 in Hw ( Fig. 12 ). Meso- and metafemora with strong spines ( Fig. 13 ).

Abdomen: Abdomen predominantly black with bright yellow markings as follows ( Fig. 3 , Fig. 13 ): S1 and S2 yellow dorsally with long yellow stripe on sides; S3 yellow dorsally with long stripe pointed apically, long yellow stripe on sides; S4–5 with a triangular basal mid-dorsal yellow spot, S4–6 with two yellow spots on sides; S7 with rectangular mid-dorsal yellow spots basally; S8–10 black; S3–8 with minute spine scattered. Superior anal appendages yellowish, slightly longer than the last segment and pointed, inferior black and rounded. ( Fig. 10 ). Subgenital plate ca. 1/2 length of S9 sternum, narrowed distally and divided deeply (nearly from its base) ( Fig. 11 ).

Description of last stadium larva. General appearance and pattern as shown in Fig. 14 .

Measurements (in mm): Total body length 19.13; length of abdomen 12.02; abdominal maximum width 6.60; head maximum width 4.08; length of hind femur 5.06; antennae third segment length 1.37; antennae fourth segment length 0.10; forefemora length 2.04; foretibiae length 2.55; midfemora length 2.80; midtibiae length 2.72; hindfemora length 5.06; hindtibiae length 3.68; epiproct length 0.73; cerci length 0.73; paraprocts length 0.86.

Coloration: Larvae uniformly dark brown, only end of femora, tibiae and tarsi with alternating yellow and dark brown bands ( Fig. 14 ).

Head: Head flat and sloping downwards, broadest across eyes. Row of three ocelli indicated as light spots obvious in ocellar triangle. Eyes large and protruding. Occipital lobe somewhat more bulging behind eyes. Antennae four-segmented, first two segments small and circular, third segment elongated, narrow proximally and becoming broader distally with outer margin a bit more convex than inner margin, which is concave. Minute setae present along both margins of third segment. Fourth segment tiny, ending with small, pointed tip ( Fig. 15 ).

Mandibles as in Figs. 16–17 and mandibular formula: L 1234 0 a(m1–5)b / R 1234 y a(m1–5)b with a>b in both mandibles. Maxillae: Galeolacinia with 7 moderately incurved teeth, three dorsal teeth nearly equal in length and robustness, three ventral teeth of same sizes, apical one largest; stipes and palp setose ( Fig. 18 ). Labium: Flat and not protruding when at rest. Prementum subquadrate ( Fig. 19 ), as long as wide (width 2.50 mm, length 2.41 mm), sides convex, convergent basally, with small teeth and minute setae at lateral margins; apical margin convex, with ventral row of 20–24 short, subquadrate reddish-brown teeth, and dorsal rows of whitish piliform setae on apical border; labial palp yellowish brown, apical lobe reddish, rounded, its internal margin with row of 12–16 equidistant teeth. Movable hook reddish-brown, sharp and moderately incurved (length 0.82 mm).

Thorax: Prothorax rectangular, dorsal portion raised at sides forming two crescent-shaped ridges. Wing sheaths parallel, reaching middle of S4. Femur and tibia of forelegs of equal length. Middle femur slightly longer than tibia. Hind femur longer than tibia. When pressed against abdomen, hind leg femur reaches basal of S6. Tarsal formula 2- 2-3, tarsi yellowish with dark band. Minute short rows of setae scattered along femur and tibia of all six legs.

Abdomen: Flat and slightly ovate. Segments of nearly equal length, except first segment reduced. Lateral edges of abdomen serrated with projecting spines which become more protrusive from S4 to S9. Abdomen with distinct pale dots and markings dorsally ( Fig. 14 ). Dorsal hooks lacking on S1–8. A small unsharp dorsal hook present on S9 ( Fig. 14 ). Anal appendages small. Epiproct and cerci of same length, paraprocts slightly longer. Epiproct triangular and pointed. Each cercus concave at outer margin and ends pointing outwards ( Fig. 20 ).

Distribution. Thailand.

Biological notes. The larva of M. thailandica occurs in headwater streams. The larvae are found in leaf litter of pool habitat. During the odonate sampling (dry season), the streams were 2.6 m wide and 36 cm in depth. The water temperature ranges from 22.5–30.6 °C, pH ranges from 6.2–7.4, dissolved oxygen ranged from 2.5–6.1 mg / L, total dissolved solids ranged from 25–114 mg /L, and conductivity ranged from 37–182 µS/cm. The larva of M. chelifer appears to be widely distributed in the Central Catchment Nature Reserve, Singapore, and is not just restricted to streams deep in the forest (Ngiam et al. 2011).

Remarks. The outstanding characters of Microgomphus larvae are 1) the third antennal segment elongated and the fourth segment vestigial, and 2) the body is ovate and much flattened dorso-ventrally. These characters in M. thailandica are similar to the three other known species of the genus ( M. chelifer , M. torquatus and M. wijaya ). The larva of M. torquatus was described by Fraser (1919) as Cyclogomphus minusculus , but Lieftinck (1940) considered that C. minusculus should be referred to Microgomphus torquatus . The larva of M. wijaya was described by Lieftinck (1940) from Sri Lanka. The successful rearing of M. chelifer allowed a larval description for M. chelifer by Ngiam (2010). Ngiam et al. (2011) stated that the larvae of M. chelifer and Heliogomphus retroflexus are very similar in antennal morphology and dorsal spine on S9. Larval morphological characters indicate that M. thailandica is closer to the larva of M. wijaya than to M. chelifer and M. torquatus . M. thailandica and M. wijaya are distinguished by the absence of dorsal hooks on the abdomen, while the other two species have conspicuous dorsal spines on all segments.

In this study, the description of M. thailandica larvae brings to five known species of gomphid larvae from Thailand ( Boonsoong & Chainthong 2014).

Figures

FIGURE 14. Microgomphus thailandica Asahina: (14) exuviae of larva, dorsal view. b Scale = 1 mm.

FIGURES 2 – 3. Microgomphus thailandica Asahina: (2) male, dorsal view; (3) female, dorsal view. Scale = 5 mm.

FIGURES 4 – 7. Microgomphus thailandica Asahina: (4) head, male, frontal view; (5) pterothoracic pattern, male, dorsal view; (6) caudal appendages, male, dorsal view; (7) caudal appendages, male, lateral view. Scale = 1 mm.

FIGURES 8 – 11. Microgomphus thailandica Asahina: (8) head, female, frontal view; (9) pterothoracic pattern, female, dorsal view; (10) caudal appendages, female, dorsal view; (11) valvula vulvae, female, ventral view. Scale = 1 mm.

FIGURE 12 – 13. Microgomphus thailandica Asahina: (12) wing venation, female; (13) pterothoracic and abdomen patterns, female, side view. Scale = 5 mm.

FIGURES 15 – 20. Microgomphus thailandica Asahina: (15) antenna, dorsal view; (16) right mandible, ventral and internal views; (17) left mandible, ventral and internal views; (18) right maxilla, ventral view; (19) ventral view of prementum; (20) dorsal view of anal appendages of exuviae. Scale = 1 mm (15, 19, 20), 0.2 mm (16, 17, 18).