Anotogaster klossi Fraser, 1919

Description of larva of Anotogaster klossi Fraser, 1919 View in CoL

( Figures 1–6 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6 , 7D View FIGURE 7 , 8 View FIGURE 8 , 9F View FIGURE 9 , 10F View FIGURE 10 )

Material examined. VIETNAM. 2 exuviae: 1 ♂, 1 ♀ (last stadium larvae when collected, then reared in laboratory), Do Quyen waterfall, Bach Ma National Park (16°11’33.8”N 107°50’54.1”E, elevation 1160 m a.s.l.), Thua Thien-Hue province, 7/IV/2024, Q.T. Phan & T.S. Keetapithchayakul leg. GoogleMaps ; 8 last stadium larvae: 2 ♂♂, 2 ♀♀, Tr’ Hy (15°49’11.0”N 107°21’45.9”E, elevation 1261 m a.s.l.), Tay Giang District , Quang Nam province, 5/VIII/2024, T.S. Keetapithchayakul leg. GoogleMaps , 2 ♂♂, 2 ♀♀, Do Quyen waterfall, Bach Ma National Park (16°11’33.8”N 107°50’54.1”E, elevation 1160 m a.s.l.), Thua Thien-Hue province, 7/IV/2024, Q.T. Phan & T.S. Keetapithchayakul leg. GoogleMaps

Description (based on 1 ♀ (last stadium larvae) from Bach Ma National Park)

Large size (48–51 mm total length), female significantly larger than male, body robust, setose and tapering caudally, with dense yellow setae, caudal appendages sharply pointed, and coloration yellow orange to reddish brown ( Fig. 1 View FIGURE 1 ).

Head. Wider than long, about 2.2 times as wide as long ( Fig. 1 View FIGURE 1 ). Labrum ( Fig. 2C, F View FIGURE 2 ), with short SS on external surface, and a dense brush of long SS along the widely concave ventral margin, flattened ventrally. Clypeus ( Fig. 2C, F View FIGURE 2 ) glabrous and moderately striated. In frontal view, anterior surface of frons, flat, glabrous and striated; in dorsal view ( Fig. 2D View FIGURE 2 ), anterior margin moderately convex, beset with a row of long, stout, thick PS, intermingled with long SS, dorsal surface covered with small scale-like setae on distal half, basal half bare. Vertex ( Fig. 2D View FIGURE 2 ) with small scale-like setae and tuff of very long SS on both sides among bordering ocelli. Antennae 7-segmented, the A3 longest, relative length of antennomeres 0.55: 0.61: 1 (1.09 mm): 0.53: 0.53: 0.61: 0.40, ( Figs 2A, C, D View FIGURE 2 , 3A View FIGURE 3 ), A1 and A2 barrel-shaped, with scattered PS, and A1–7 with scattered SS. Compound eyes ( Fig. 2A, C View FIGURE 2 ) poorly developed, protruding latero-dorsally. Occiput ( Fig. 2A View FIGURE 2 ) large and laterally rounded, with long, stout, thick PS, intermingled with long SS and SPS on lateral margin, densely covered with scale-like setae on dorsal surface; postocular lobe ( Fig. 2A View FIGURE 2 ) poorly developed, forming slightly straight on posterior margin. Genae ( Fig. 2B, E View FIGURE 2 ) with row of long SS arranged in a line on inner margin; with long, SPS, intermingled with long SS on ventral surface of compound eyes. Labium ( Figs 1B View FIGURE 1 , 3B, C View FIGURE 3 ) spoon-shaped, ventral surface covered with delicate, long SS; prementum-postmentum articulation reaching middle of metacoxae. Prementum ( Fig. 3B, C View FIGURE 3 ) subpentagonal, latero-basal margins slightly concave, lateral margins with two rows of SPS, those of ventral row minute and same size, those of dorsal row small, increasing in size apically and meeting at base of palp’s articulation; with a longitudinal, central sulcus and scattered long SS on ventral surface; premental setae ( Fig. 3B View FIGURE 3 ) with 7 long and 3–4 short premental setae (7+3, 7+4) to each side of midline; ligula ( Fig. 3D View FIGURE 3 ) poorly-developed, slightly concave in shape, with a V-shaped median process on the apical margin, and a dense row of small PS on apical border excepting the median process which is serrulated on mesal margins ending in a sharp tip; additional small, serrulated, blunted or pointed process at base of each branch of median process; labial palp ( Fig. 3E, F View FIGURE 3 ) strongly developed, covering anterior part of head as a mask, not covering the frons ( Fig. 8B View FIGURE 8 ), the apical margin irregularly toothed, forming 11–14 short, pointed hooks of different size and robustness, all of which have a fine serration on margins; dorsal margin of each palp fringed with dense rows of long SPS, ventral surface dividing to two regions by small setae: setose region (scattered stout SS) on dorsal side, covering 3/4 and glabrous region; with 1 short and 5 long palpal setae; movable hook slender, sharply pointed, smooth. Mandibles ( Fig. 4A–H View FIGURE 4 ) with formula: L 12340 View Materials a(m 1,2,3) b, with incisors 1> 2> 3> 4; R 12345 y a(m 1,2,3,4,5) b, with incisors 1> 2> 3> 4>5, asymmetrical, robust with well-developed long teeth, m denticles small, blunt, semi-fused forming a continuous ridge; outer margin of mandible smoothly angulate without obvious spines, bearing antero-laterally long SS. Maxilla ( Fig. 4I–K View FIGURE 4 ) galeolacinia with 7 teeth, 4 dorsal teeth of approximately the same size, apical tooth largest, 3 ventral teeth of small size, with one smallest tooth on the apical tooth.

Thorax ( Figs 1 View FIGURE 1 , 7D View FIGURE 7 , 8 View FIGURE 8 ). Narrower than head, covered densely by minute scale-like setae. Prothorax with dense SS on propleura, pronotum anterior margin almost straight, posterolateral margins wavy, middle part of posterior margin produced caudally as a “pull flap”, transverse pronotal disc beset with long, stiff SS on posterolateral margins, posterior margin forming subtle ridge across posterior border. Pterothorax with dense SS on pleura; notum with white dorsal area of mesopleura shield-like, with a pair of large transverse spiracles. Wing sheaths divergent; anterior and posterior wing sheaths reaching posterior margin of S3 and basal half of S4, respectively. Legs ( Fig. 5 View FIGURE 5 ) coxa robust; femora moderately thick, elongated, covered with dense long SS; tibia slender than femora, slightly curved, with scattered SS and SPS towards distal end; tibial comb of foreleg with numerous robust, short, blunted SPS; tibial comb of mid- and hindlegs with a row of robust, short SPS and a row of SS; tarsal formula: 3-3-3, pretarsal claw simple, with well-developed empodium, pretarsal claw of hindleg slightly larger than other legs; tarsi of all legs with a row of robust, short, blunted SPS on mesal margin and scattered SS.

Abdomen ( Figs 1 View FIGURE 1 , 6 View FIGURE 6 , 7D View FIGURE 7 , 8 View FIGURE 8 ). Cylindrical, strongly tapering caudally. Terga covered with abundant, small SS, and dense long, fine SS on sides. Posterior margins of S2–9 with a row of small SS intermingled with long SS, scattered SPS; posterior margin of S10 slightly serrate. Lateral area of terga S1–5 with dense, long SS; lateral area of terga S5–10 with dense, long SS and row of SPS; lateral margins of S8–9 ending in a convergent, acute spines ( Fig. 6D View FIGURE 6 ). Sterna S1–10 covered abundantly with small SPS; posterior margins of sterna S1–6 with a row of short PS, on S7–10 with short PS and SPS; sterna 2–8 divided into three sternites, sternum S9 consisting of only one sternite, and sternum 10 forming a continuous ring with respective tergum. Female gonapophyses ( Fig. 6D–E View FIGURE 6 ) well-developed, smoothed, surpassing beyond posterior margin of sternum S9. Caudal appendages ( Fig. 6A–C View FIGURE 6 ), tips long and acutely pointed, pyramidal shape, slightly downcurved. Epiproct 0.94x as long as paraprocts, with abundant long SS on outer and medial margins. Paraprocts with a row of six stout SPS along lateral surface, with dense long SS on inner margins; cerci conical, acutely pointed, 0.20 as long as epiproct length.

Description of male larva. As female, unless otherwise stated: large size (41–46 mm total length), male gonapophyses poorly-developed; male epiproct with a basal, mound-like dorsal tubercle.

Habitat and biology. The larvae of A. klossi inhabit small forest streams, with pools or areas of slow-moving water ( Fig. 7A–C View FIGURE 7 ). The streambed where collections were made consisted of mud/silt (40%), small stones/pebbles/ gravel/sand (20%), leaf litter (25%), and riparian/root tree debris (15%). The larvae hide themselves under small rocks, slit and leaf litter. The larval coloration acts as camouflage, allowing them to blend seamlessly with their surroundings ( Figs 7B View FIGURE 7 , 8A View FIGURE 8 ). The larvae were found coexisting with the larvae of Davidius sp. , Chlorogomphus spp. , Heliogomphus spp. , Megalestes australis Karube, 2014 , Euphaea saola Phan & Hayashi in Phan, Kompier, Karube & Hayashi, 2018, Cryptophaea vietnamensis ( van Tol &Rozendaal, 1995) , Coeliccia scutellum Laidlaw, 1932 , and Copera marginipes ( Rambur, 1842) ( Phan & Keetapithchayakul 2023, 2024; Keetapithchayakul & Phan 2024). Some specimens had 1–2 chironomid larva attached in the space between wing sheaths or groove between pronotum and dorsal mesopleura in a phoretic association ( Fig. 7D–E View FIGURE 7 ). The larvae exhibit a specialized ambush predation strategy characterized by inhabiting muddy or sandy substrates while remaining partially buried or motionless, blending seamlessly into their surroundings. This behavior reduces detection by both predators and prey, including instances of cannibalism ( Figs 7B View FIGURE 7 , 8A View FIGURE 8 ). Additionally, they displayed agonistic behaviour, characterized by the tendency to hold the distal end of the abdomen slightly upturned, while the caudal appendage was displayed and pointed upwards ( Fig. 8B View FIGURE 8 ).