Onychogomphus castor Lieftinck, 1941

Chainthong, Damrong & Boonsoong, Boonsatien, 2016, Description of two final stadium Onychogomphus larvae from Thailand (Odonata: Gomphidae), Zootaxa 4066 (5), pp. 561-570 : 562-565

1. Onychogomphus castor Lieftinck, 1941

( Figs. 1 , 3–12)

Material examined (5 F0, 2 ♀, 3 ♂): 1 F0 larva, 30.III.2013, Kang Som Meaw (13°24′28″ N 99°16′ 52″E, altitude 200 m), Suanpung district, Ratchaburi province, Thailand, D. Chainthong leg.; 1 ♀ and its exuvia, emerged on 24.IV.2013. 3 F0 larvae, 4.II.2014, Huai Khayeng (14°36′20″ N 98°34′ 38″E, altitude 206 m), Thong Pha Phum district, Kanchanaburi province, Thailand, D. Chainthong leg.; 1 ♀, 2 ♂ and their exuviae, emerged on 18.V.2014, 24.IV.2013, 18.V.2014. 1 F0 larva, 14.XII.2014, Huai Pak Kok (14°39′34″ N 98°32′ 02″E, altitude 176 m), Thong Pha Phum district, Kanchanaburi province, Thailand, D. Chainthong leg.; 1 ♂ and its exuvia, emerged on 18.III.2015.

Coloration: Larvae uniformly bright yellow, body stout and bulky, integument finely granulose, body covered with hair-like setae ( Fig. 1 ).

Measurements (n=5): Total body length 28.18 mm, length of abdomen 14.1 mm, abdominal maximum width 6.7 mm, head maximum width 5.3 mm, length of hind femur 3.4 mm, length of epiproct 1.9 mm, length of paraprocts 2.0 mm, length of cerci 1.5 mm.

Head: wider than long, frontal part more stout, posterior lobe of the head as long as the eye, eyes large and broadest across, with three large ocelli. Antennae: Four-segmented, first two segments short and rather circular, third segment largest and scoop-shaped (length 1.3 mm), fourth segment tiny (length 0.1 mm), with many long setae densely distributed on antennae ( Fig. 4 ). Mandibles as in Figs. 5–6 with formula: L 1234 0 a(m1–6)b / R 1234 y a(m1–3)b with a>b in both mandibles. Maxilla: galeolacinia with seven moderately incurved teeth, three dorsal teeth nearly equal in length and robustness, three ventral teeth of same size, apical one largest; stipes and palp very strongly setose ( Fig. 7 ). Labium: flat and not protruding when at rest ( Fig. 8 ). Prementum-postmentum articulation reaching posterior margin of procoxae. Prementum subrectangular, longer than wide, length 3.9 mm, width 2.8 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 with uniformly inflexed inner edge, yellowish brown, apical lobe reddish, rounded, internal margin with row of 15–18 equidistant teeth. Movable hook reddish brown, sharp, and moderately incurved (length 0.9 mm).

Thorax: Small, prothorax narrower then head, dorsal portion raised at sides forming two U-shaped ridges. Wing sheaths strongly divergent, reaching S5 (inner wing pads length 5.1 mm, outer wing pads length 4.3 mm). Legs short and stout, fore and middle legs strongly curved; protibiae (length 2.2 mm) decidedly longer than profemora (length 1.9 mm); mesotibiae (length 2.3 mm) slightly longer than mesofemora (length 2.1 mm); metafemur slightly longer than metatibia. Tarsal formula 2-2-3, tarsi yellowish. Minute short rows of setae scattered along femur, tibia, and tarsus of all six legs.

Abdomen: less convex dorsally, bright yellow, with distinct pale dots and markings ( Fig. 10 ). Mid-dorsal spines, absent on S1 and most conspicuous on S2–9, largest mid-dorsal spine on S9 ( Fig. 11 ). Lacking lateral spines on S2–5. Lateral edges of abdomen serrated with projecting spines that become more protrusive on S6–9 ( Figs. 10–11 ). Sternites finely granulose, yellow, with pale spots on outer plates, sternite 8 divided in 5 plates, remainder in 3 plates, median sutures of sternites slightly convergent apically on 2, parallel on 3–4 and gradually divergent on 5–9, posterior margin of sternites 1–9 straight, wavy on 10 ( Fig. 12 ). Spiracles are visible on S2–8. No lateral spine and no dorsal hook on S10. Anal appendages elongated. Epiproct same length as paraproct, cerci shorter; epiproct narrowly triangular, conical. The outer margin of the paraproct slightly concave at the base. Each cercus concave at outer margin ( Fig. 9 ).

Figures

FIGURES 1 – 2. Onychogomphus castor Lieftinck and O. duaricus Fraser, respectively: habitus of larvae, dorsal view.

FIGURES 4 – 9. Onychogomphus castor Lieftinck: (4) antenna, dorsal view; (5) right mandible, ventral and internal views; (6) left mandible, ventral and internal views; (7) right maxilla, ventral view; (8) ventral view of prementum; (9) dorsal view of anal appendages. Scale = 1 mm (4, 8, 9), 0.5 mm (5, 6, 7).

FIGURES 10 – 12. Onychogomphus castor Lieftinck: (10); right side of abdomen of exuvia, dorsal view; (11) lateral view of abdomen in exuvia; (12) ventral view of abdomen. Scale = 1 mm.