Amphigomphus somnuki Hämäläinen, 1996

Novelo-Gutiérrez, Rodolfo & Sites, Robert W., 2019, The larva of Amphigomphus somnuki Hämäläinen, 1996 and the first records of the genus Stylogomphus Fraser, 1922 for Thailand (Odonata: Gomphidae), Zootaxa 4555 (1), pp. 121-126 : 122-126

Amphigomphus somnuki Hämäläinen, 1996

Figs. 1–6A .

Material studied: One exuvia (♂ emerged), 96 larvae (43 F-0, 1 F-1?, 5 F-2?, 47 mixed young instars). THAILAND: Mae Hong Son Province: Namtok Maw Pang, 14 Oct 2002, 850 m, 19°22'N 98°22'E, CMU team leg., 6 young larvae; same data but Namtok Mae Surin National Park, stream from Mae Surin Waterfall , 1 Apr 2003, 1132 m, 18°56'N 98°36'E, UMC and CMU teams leg., L-434, 2 F-0. Chiang Mai: Doi Inthanon National Park , Huay Sai Luang Waterfall, 1060 m, 18°31'N 98°27'E, 3 Mar 2002, J. Naewong leg., 1 F-0 ; same data but 20 Mar 2002, R. W. Sites, A. Vitheepradit, Kirawanich leg., L-312, 1 F-0 ; same data but 4 Apr 2002, UMC and CMU teams, L-322, 1 F-0 ; same data but 9 Jun 2002, P. Thamasenanupap leg., 3 young larvae ; same data but stream 200 m west of Huay Sai Luang Waterfall , L-323, 2 F-0 ; same data but Mae Klang River at Ecolodge , 1000 m, 8 May 2002, 18°32'N 98°32'E, UMC and CMU teams leg., L-399, 1 F-0 ; same data but 13 Mar 2003, CMU team leg., 1 F- 0 ; same data but 2 Apr 2003, UMC and CMU teams leg., L-437, 1 F-0 ; same data but Siriphum Waterfall , 1380 m, 26 Jun 2002, 18°32'N 98°31'E, R. W. Sites leg., L-412, 1 middle-aged larva ; same data but Nam Mae Aep above road 1009, stream, 630 m, 6 Jul 2002, 18°32'N 98°32'E, CMU team leg., 4 young larvae (gravel) ; same data but 12 Jan 2003, UMC and CMU teams leg., 2 F-2 ?; same data but Mae Pan Noi at Ban San Pathana , bedrock stream, 750 m, 22 Sep 2002, 18°31'N 98°25'E, CMU team leg., L-446, 5 young larvae ; same data but 14 Jan 2003, UMC and CMU team leg., 1 F-0 and several young larvae); 17 Feb 2003, CMU team leg., 2 F-0 ; same data but 15 Mar 2003, UMC and CMU teams leg., 1 F-0 ; same data but 4 Apr 2003, UMC and CMU teams leg., 1 F-0 ; same data but Mae Klang River at Namtok Sob Ab , 12 Jan 2003, 1000 m, 18°32'N 98°32'E, CMU team leg., 1 F-1 ?; same data but Mae Klang River at Sob Ab Waterfall, 543 m, 18°31'N 98°36'E, UMC and CMU teams leg., 1♂ teneral emerging and exuvia. Doi Suthep-Pui National Park , Huay Kaew above lower falls at Namtok Monthathan, 750 m, 5 Mar 2002, 18°49'N 98°55'E, R. W. Sites, Kirawanich leg., L-261, 3 F-0 ; same data but Sai Yoi Waterfall , 1100 m, 18°48'N 98°55'E, 5 Apr 2002, UMC and CMU teams leg., L-326, 1 F-0; 8 Oct 2002, Sites, Vitheepradit, Prommi, Setaphan leg., 5 young larvae ; same data but 14 Feb 2003, Sites, Vitheepradit, Prommi, Setaphan leg., 2 F-0 ; same data but 4 Apr 2003, Sites, Vitheepradit, Prommi, Setaphan leg., L-447, 1 F-0 ; same data but Namtok Monthathan , 700 m, 8 Apr 2002, 18°49'N 98°55'E, UMC and CMU teams leg., L-330, 1 F-0 ; same data but 9 Aug 2002, P. Thamasenanupap leg., 1 F-0 in leaf packs ; same data but 29 Mar 2003, UMC and CMU teams leg., L-427, 2 F-0, 1 young larvae in gravel ; same data but 29 Apr 2003, A. Vitheepradit, P. Thamasenanupap, M. Ferro leg., L-489, 2 F- 0 ; same data but Pa Ngerb stream, 530 m, 5 Apr 2002, 18°48'N 98°56'E, UMC and CMU teams leg., 2 F-0, 2 young larvae ; same data but 29 Mar 2003, UMC and CMU teams leg., 2 F-0 ; same data but 15 Nov 2002, CMU team, 1 F-0. Fang Horticulture Experiment Farm, Nam Mae Chai, 600 m, 17 Mar 2002, 19°57'N 99°09'E, R.W. Sites, A. Vitheepradit, Kirawanich leg., L-301, 1 F-0. Chiang Dao Wildlife Research Center, creek, 520 m, 18 Mar 2002, 19°21'N 98°55'E, R.W. Sites, A. Vitheepradit, Kirawanich leg., L-303, 1 F-0. Amphur Mae Chaem, Mae Pan, 14 Jan 2003, 540 m, 18°31'N 98°23'E, UMC and CMU teams leg., 3 F-2?; Amphur Mae Rim, Mae Sa Waterfall, 1030 m, 18°52'N 98°48'E, 6 Apr 2002, UMC and CMU teams leg., 2 F-0 larvae in gravel. Kanchanaburi: Thong Pha Phum Nat. Pk., Huay Pak Kog, 1 Jun 2011, 139 m, N 14° 47.183', W 98° 48.401', R.W. Sites leg., L-1303, 12 mixed age larvae. Phayao: Doi Luang National Park , Namtok Cham Pa Thong, 2002-2003, 620 m, 19°13’N 99°44’E, CMU team leg., 5 young larvae. Lampang: Chae Son National Park , Namtok Chae Son, 25 Oct 2002, 650 m, 18°50'N 99°28'E, CMU team leg., 3 young larvae. Phitsanulok: Phu Hi Rongkla National Park, Waterwheel Falls , 10 Mar 2002, 1280 m, 16°59’N 101°00’E, Sites, Vitheepradit, Kirawanich leg., 2 F-0, 6 younger larva gravel-sand ; same data but 22 Apr 2002 CMU team leg., 1 F-0 ; same data but 21 Jun 2002, young larvae; 17 Mar 2003, 1 F-0, 4 young larvae ; same data but Namtok Huai Khamuen Noi , 17 Jan 2003, 1220 m, 16°59’N 101°00’E, CMU team leg., 1 F-0 and 1 very young larva. Loei; Amphur Lom Sak, 62 km E of Lom Sak on Hwy 2016, 24 Jun 1998, [no elevation or coordinates], A. Vitheepradit & Sawangsak leg., L-208, 1 F-0 .

Description. Final instar: Medium size (TL 24.3¯26.5), body robust, setose laterally, abdomen fusiform with dorsal protuberances on S2-9, and yellow-brown coloration with brown spots ( Fig. 1 ).

Head. Head wider than long, narrower than synthorax and abdomen. Labrum 0.5 mm long, anterior border densely setose and flattened ventrally. Anteclypeus bare, postclypeus and frons covered with robust, stiff setae of different sizes; vertex and occiput with small, stout setae. Antennae densely covered with small, scale-like setae on dorsal surface and fringed with long white setae on lateral margins, scape globose, pedicel subglobose; 3rd antennomere largest, cylindrical, parallel-sided, three times longer than wide, with a circular tuft of long setae distally; 4th antennomere a conical rudiment. Compound eyes moderately developed. Posterior margin widely concave, occipital lobes rounded and bulging. Mandibles ( Fig. 2 ) with formula: L 1234 0 a(m 1,2,3)b/ R 1234 y a(m 1,2)b. Galeolacinia of maxilla ( Fig. 3 ) with seven moderately incurved teeth: three dorsal teeth approximately same length and robustness; four ventral teeth of different sizes, apical tooth largest. Ventral pad of hypopharynx subpentagonal ( Fig. 3 ), whitish, mostly soft and bare, with a transverse basal sclerite that extends laterally as a digitate branch along basal half of pad. Labium: Prementum-postmentum articulation reaching posterior margin of procoxae ( Fig. 1C ). Prementum light yellow-brown, longer than greatest width, ratio length to width 1:0.83, parallel-sided in apical 0.40, with a row of minute scale-like setae on each side; without ventral sulcus; ligula poorly developed ( Fig. 4 ), with apical margin convex, dorsal double row of piliform setae, and ventral row of 27 or 28 small, truncate, reddish teeth. Labial palp yellowish red, with apex rounded and mesal margin beset with 13–15 small, truncate teeth; movable hook yellowish red, shorter than palp, sharp and moderately incurved ( Fig. 4 ).

Thorax. Prothorax narrower than head, setose on ventral border. Pronotum covered with minute dark setae except on large, dorsolateral, bare, irregular areas; anterior margin wavy, lateral margins rounded, posterior margin widely convex. Synthorax yellow with sutures dark, densely setose on ventrolateral areas. Legs short (e.g., when fully extended, hind legs not reaching posterior margin of S7), strongly setose, mainly on fore- and middle legs; burrowing hooks lacking; claws simple, chelate-like on fore- and middle pretarsi, long and sharp on hind pretarsi, with a pulvilliform empodium. Wing sheaths strongly divergent, with setae on margins, remainder of surface mostly bare; fore and hind wing sheaths reaching basal half and posterior margin of S4, respectively.

Abdomen. Fusiform, with dorsal surface convex, ventral surface more or less flat, yellow, with a complex pattern of pale and dark spots on S5–10, prominent large dark marking on S6 and longitudinal parallel stripes on S10 ( Fig. 1A ), with dorsal protuberances on S2–9, those on S2–3 short and more vertical than the others, those on S4–9 low, roundly pointed and directed caudad. Terga 2–10 with abundant minute setae, and some long, scattered, stiff setae on S2–9, including posterior margins; lateral margins of S2–10 setose, serrate on S6–9, those on S7–9 ending in sharply pointed posterolateral spines of approximately same size and robustness ( Fig. 1B ). Sterna 1–8 light yellowish-brown, 9–10 slightly darker. Sterna 1–7 and 9 divided into three sternites, sternum 8 divided into five sternites ( Fig. 5 ). Female gonapophyses vestigial, bilobed, lobes conical with apices rounded, the space in between equal to the basal width of each lobe. Caudal appendages longer than dorsal length of S9+10, sharply pointed, densely covered with minute spiniform setae; epiproct feebly decurved at tip, slightly longer than paraprocts, cerci slightly shorter than epiproct ( Fig. 1B ); male epiproct with a pair of dorsolateral tubercles at 0.65 length of epiproct.

Measurements: TL 24.3¯26.5; AL (ventral) 15.1¯16.6; MWh 5.0¯5.2; HfL (lateral) 3.8¯4.0; Ep 1.9–2.0, Pp 1.8–1.9, Ce 1.7–1.9.

Diagnosis. The larvae of the three known species of Amphigomphus are extremely similar, making their separation difficult. The larva of A. somnuki is the smallest ( A. nakamurai TL 30.45, A. hansoni 28.4¯30.3), and differs from A. nakamurai mainly by the caudal appendages densely covered with minute spiniform setae (almost smooth in A. nakamurai ), and from A. hansoni by the male epiproct with the dorsal tubercles at basal 0.65 [approximately at basal 0.40 according to figures 1 and 6 in Xu (2012)].

Habitat. The larvae of A. somnuki inhabit small streams among gravel, gravel-sand and leaf pack substrates. Xu (2012) found larvae of A. hansoni buried deeply in sand.

Distribution and new records. In Thailand, Amphigomphus somnuki has been recorded only from the province of Chiang Mai ( Hämäläinen 1996; Hämäläinen & Pinratana 1999, 2000). We collected larvae of this species from mountain streams in western and northern Thailand and provide new province records for Kanchanaburi, Lampang, Loei, Mae Hong Son, Phayao, and Phitsanulok ( Fig. 6A ).

Figures

FIGURE 1. Habitus of last instar Amphigomphus somnuki. (A) dorsal, (B) lateral, (C) ventral.

FIGURES 2–5. Structures of larvae of Amphigomphus somnuki. (2) ventral surface of right (a) and left (b) mandibles, (3) ventral surface of head showing maxillae and hypopharynx, (4) ventral surface of prementum showing ligula and palps, (5) abdominal sterna 7–9 (yellow arrow indicates anterolateral suture).

FIGURE 6. Larval collection records of (A) Amphigomphus somnuki (yellow circles) and (B) Stylogomphus sp. (white circles).