Heliogomphus selysi Fraser, 1925

Boonsoong, Boonsatien & Chainthong, Damrong, 2014, Description of the final-instar larva of Heliogomphus selysi Fraser (Odonata: Gomphidae), Zootaxa 3764 (4), pp. 482-488 : 483-486

Heliogomphus selysi Fraser, 1925

( Figs. 1–13 )

Material examined: 4 final stage larvae, 30.III.2013, Borwee waterfall (13°28.6’N, 99°14.5’E), Suanpung district, Ratchaburi province, Thailand, D. Chainthong leg.; 1 ♂ and exuvia, emerged on 16.IV.2013; 1 ♂ and exuvia, 24.IV.2013; 2 ♂ and exuviae, 9.V.2013.

The identification of male adult of H. selysi was confirmed based on Asahina (1986) using the following key characters: head, pterothoracic pattern, and caudal appendages ( Figs. 1–4 ).

Coloration: Larvae uniformly dark brown, only tarsi yellow ( Fig. 5). Total body length 18.4–19.4, abdomen length 10.9–12.9, abdomen maximum width 5.9–6.2, head maximum width 4.4–4.7, hind femur length 3.9–4.3.

Head: Head flat and sloping downwards, broadest across eyes. Occipital lobe somewhat more rounded behind eyes. A row of three ocelli indicated as light spots obvious in ocellar triangle. Eyes large and protruding. Head much projecting in front, frontal lobe very broad. Antennae very distinct, each about 1.89 mm in length. First two segments small and cylindrical. Third segment enlarged (length 1.5), plate-shaped ( Fig. 6 ). Minute, scale-like and much enlarged setae present along both margins of third segment. Fourth segment absent. Labium flat, not protruding in front when contracted. Mandibles as in Figs. 7–8 , mandibular formula: L 1234 0 a(m1–7)b / R 1234 y a(m1–6)b with a>b in both mandibles. Maxillae: Galeolacinia with 7 moderately incurved teeth, three dorsal teeth nearly equal length and robustness, three ventral teeth of same sizes, apical one largest; stipes and palp very strongly setose ( Fig. 9 ). Labium: Prementum-postmentum articulation reaching posterior margin of procoxae. Prementum subquadrate ( Fig. 10 ), as long as wide (width 2.9, length 2.8), sides convex, convergent basally, with short setae at lateral margins; apical margin convex, with ventral row of 19–21 short, subquadrate reddish-brown teeth, and dorsal rows of whitish piliform setae on apical border; labial palp yellowish-brown, apical lobe reddish, rounded, internal margin with row of 10 equidistant teeth. Movable hook reddish-brown, sharp and moderately incurved (length 0.75).

Thorax: Prothorax rectangular, divided into upper and ventral parts, dorsal portion raised at sides forming two crescent-shaped ridges. Wing sheaths parallel, reaching abdominal segment S4, anterior wing pads slightly surpassing posterior margin of S4, posterior ones reaching basal half of S5 (inner wing pads length 5.1, outer wing pads length 4.6). Legs widely distant, rather short and flattened. Tibiae of fore legs decidedly longer than femora (fore femora length 2.3, fore tibiae length 3.2). Mesotibiae slightly longer than mesofemora (mid femora length 2.8, mid tibiae length 3.1). On hind leg, femora slightly longer than tibiae. When pressed against abdomen, hind leg femur reaches end of S5. Tarsal formula 2-2-3, tarsi yellowish.

Abdomen: Abdomen flat and slightly ovate. Segments nearly equal in length, excepting first segment which is reduced. Sides of abdomen with weakly developed projecting spines that become more curved from S7–9. Side margin of S9 finely denticulate. Abdomen with distinct pale dots and markings dorsally ( Fig. 11 ). Dorsal hook unsharpened, absent on S1–3 and most conspicuous on S4–9, most protuberant on S8–9 ( Fig. 12 ). No lateral spines and no dorsal hooks on S10. Anal appendages small. Epiproct (0.6) and cerci (0.5) of nearly equal length, paraprocts slightly longer (0.8). Epiproct triangular and lancet-like pointed. Each cercus concave at outer margin with ends pointing outward ( Fig. 13 ).

Biological notes. The larvae of Heliogomphus occur in headwater streams, where they are found in leaf litter of pool habitat. During odonate sampling (dry season), the streams were about 2.6 m wide and 36 cm in depth. Water temperature ranged from 22.5–30.6 °C, pH from 6.2–7.4, dissolved oxygen from 2.5–6.1 mg /L, total dissolved solids from 2.5–11.4 mg /L, and conductivity from 37–182 µS/cm.

Figures

FIGURES 1 – 4. Heliogomphus selysi: (1) head, male, frontal view; (2) pterothoracic pattern, male, dorsal view; (3) caudal appendages, male, dorsal view; (4) caudal appendages, male, lateral view. Scale = 1 mm.

FIGURES 6 – 13. Heliogomphus selysi: (6) antenna, dorsal view; (7) right mandible, ventral and internal views; (8) left mandible, ventral and internal views; (9) right maxilla, ventral view; (10) ventral view of prementum; (11) lateral view of abdomen in exuviae; (12) left side of abdomen of exuvia, dorsal view; (13) dorsal view of anal appendages of exuvia. Scale = 1 mm (6, 10, 11, 12), 0.2 mm (7, 8, 9), 0.5 mm (13).