Platycnemis phasmovolans Hämäläinen, 2003

Keetapithchayakul, Tosaphol Saetung & Phan, Quoc Toan, 2024, Description of the larva of Platycnemis phasmovolans Hämäläinen, 2003 (Odonata, Platycnemididae), with a key to the larvae of the subfamily Platycnemidinae from the Sino-Japanese and Oriental regions, ZooKeys 1221, pp. 1-18 : 1-18

Platycnemis phasmovolans Hämäläinen, 2003

Material examined (larva).

Vietnam • 1 exuviae: 1 ♂ (collected as last stadium larva, reared in laboratory); 27 Jul. 2024; 18 ° 59 ' 24.4 " N, 104 ° 50 ' 17.8 " E; elevation 266 m a. s. l.; Yen Khe Commune , Con Cuong District, Nghe An Province; T. S. Keetapithchayakul leg.; ZCDTU . • 7 late stadium larvae: 1 ♂ (F- 0), 1 ♀ (F- 0), 1 ♂ (F- 1), 2 ♀♀ (F- 1), 1 ♂ (F- 2), 1 ♀ (F- 2); 27 Jul. 2024; same site and collector as above; ZCDTU . • 2 early stadium larvae: 1 ♂, 1 ♀; 27 Jul. 2024; same site and collector as above; ZCDTU .

Description of larva.

(based on 1 male (exuviae) and 1 female (F- 1 )) Habitus (Fig. 2 ) slender and elongate, long thin legs, abdomen cylindrical, slightly tapered caudad, lamellae of caudal gills with terminal filament at apex; coloration varies from yellowish-brown to bright green brownish to brownish-black.

Head: broad in dorsal view, roughly a strongly squashed pentagon in outline, with hind margin strongly excavated; bearing scattered simple setae; labrum flattened ventrally, outline with convex corners flanking central anterior concavity, with minute tubercles on distal half and basal glabrous; frons and vertex strongly raised with prominent ocelli; compound eyes narrow and rounded protruding postero-laterally; occiput with dense minute tubercles and scattered simple setae, convex in outline, anterior occiput with low raised prominences just behind margin of eyes (Fig. 3 , indicated by red arrows); postocular lobes, rounded, scattered simple setae on anterior margin, with scattered papilliform setae and robust spiniform setae on posterior margin; genae (Figs 3 B , 5 A ) with row of 2–3 blunt stout spines and simple setae on anterolateral margin. Antennae (Fig. 4 A ) filiform, 7 - segmented with A 2 the longest, relative length of antennomeres 0.93: 1 (0.4 mm): 0.95: 0.85: 0.58: 0.4: 0.33. Prementum (Fig. 4 B ) elongate subpentagonal shape, its basal hinge reaching anterior of mid coxae when mask folded; with two pairs of strong premental setae; lateral margin at base of palp with 3–4 distinct spiniform setae; with a row of 16–18 spiniform setae along distal half of lateral margin, with 1 pair long thin simple setae on middle of ventral side (Fig. 4 C ); ligula (Fig. 4 F ) strongly produced to form an obtuse angle, the two sides slightly convex; with one pair of short subapical protuberances and minute spiniform setae along margin; lobe of labial palp (Fig. 4 D ) 0.41 length of prementum with 4 setae on palpal lobe, outer margin with row of short spiniform setae, inner margin with weakly crenate; apex with 2 processes, the outer one truncate, but with a distinctly slanted or curved margin and bearing 5 distinct teeth, the innermost being largest and most isolated; inner process tapered then abruptly narrowed to thin acutely tipped end hook (Fig. 4 E ); movable hook slender and about 0.60 times as long as palpal lobe, acuminate, bent slightly inwards. Maxilla (Fig. 5 B, C ) galeolacinia with 7 teeth, 4 dorsal teeth approximately of the same size, apical teeth largest, 3 ventral teeth of small size. Mandible (Fig. 5 D – G ) with mandibular formula: L 1 + 1 ’ 234 a b / R 1 + 1 ’ 234 y a, asymmetrical, robust with well-developed long teeth on each incisor lobe; left mandible with five incisor teeth, two molar teeth (a = b); right mandible with five incisor teeth, one molar tooth, an additional tooth.

Thorax: narrower than head, with scattered simple setae, papilliform setae, and white spots. Prothorax dorsally flattened; lateral angles acute, projecting sharply at postero-lateral corners; posterior margin gently keeled midline, forming subtle ridge across posterior border, rounding at lateral edges. Synthorax robust, slightly elongated; mesepisternum with pronounced lateral keels defining boundary with mesepimeron; keels slightly raised, forming well-defined ridge; dorsal surface of mesepisternum with faint longitudinal ridges, aligned parallel to midline; mesinfraepisternum slightly convex; wing pads pale with glabrous, parallel, anterior and posterior wing pads reaching to distal margin of S 6; legs almost flat and long; femora thin with dark band on posterior side, row of spiniform setae and scattered simple setae; tibial comb with scattered setae and a few tridentate setae; two claws simple with pulvilliform empodium.

Abdomen: cylindrical, slender, narrowing caudally, scattered simple setae, minute tubercles and white spots; abdominal terga with pale longitudinal line, posterior margin with pair of pale black spots; abdominal sterna smooth; abdominal pleura flatted on S 2 – S 9, with scattered simple setae, and row of spiniform setae and simple setae on lateral margin, lateral spines on abdominal S 5 – S 9 (S 9 ≥ S 8 ≥ S 7> S 6 >> S 5) (Fig. 6 A ). S 10 with cluster of spiniform setae externally at the basal of cerci; male gonapophyses (Fig. 6 B, C ) broad-based, conical, sharply pointed, slightly divergent in ventral view, almost reaching anterior margin of S 10, with a row of simple setae on ventral margin; gonopore small, O-shape embossed with median fissure; female gonapophyses (Fig. 6 D, E ) with two pairs of long valvae; lateral valvae terminating in sharply pointed processes, slightly divergent, with a distinct postmedian ventral spine preceded by row long simple setae on each side, extending over sternite 10; central valvae longer than lateral valvae, smooth, slender, apically rounded. Caudal lamellae (Fig. 7 ) long and narrow, lanceolate, with irregular light and dark-brown markings, rather sparse spiniform setae and simple setae of variable lengths along margin, median trachea; terminal filament pale and slim; a distinct median trachea with spiniform setae array on both sides, reaching terminal filament; median lamella only slightly shorter and broader than lateral lamella.

Material examined (adult).

Vietnam • 4 ♂♂; 21 May 2024; 18 ° 59 ' 24.4 " N, 104 ° 50 ' 17.8 " E; elevation 266 m a. s. l.; Yen Khe Commune , Con Cuong District, Nghe An Province; Q. T. Phan leg.; ZCDTU . • 3 ♂♂, 2 ♀♀; 27 Jul. 2024; same site and collector as above .

Additional observations (adult).

China • 1 ♂ 26–31 May 2020; 25 ° 18 ' 36.0 " N, 107 ° 54 ' 00.0 " E; Maolan National Nature Reserve , Guizhou, Libo County, Province, Ruibin Song observer .

Brief description of adult.

Male (Fig. 8 A ) – Head: black with broad bluish transverse stripe across frons and genae, broken in middle above pale blue postclypeus (Fig. 1 A ). Thorax: prothorax black with paired blue lateral markings on pronotum with irregular inner margins; propleuron entirely black (Fig. 1 C ); synthorax black with narrow blue antehumeral stripes, two distinct lateral stripes: one pale blue on metepisternum, the other tending to very pale blueish-yellow on lower margin of metepimeron (Fig. 1 C ); fore legs with femora white, except anterior side which is black in the apical third; tibiae and tarsi black; mid and hind legs with femora and tibiae wholly white, tibiae enormously dilated, feather-like, length 2.87 times and 3.22 times maximum width, respectively. Abdomen: black with blueish-white pattern: S 1 with heart-shaped spot laterally; S 2 with narrow stripes along lower margin and 1–2 markings above stripes; S 3-6 with basal rings, concave dorsally, smallest on S 3 and largest on S 6, that on S 3 incomplete dorsally; S 6 marking one-third length of segment; S 7 with ventro-lateral basal marking; S 8–9 entirely black; posterior half of S 10 dorsum blue to pale yellowish (Fig. 1 G ); appendages pale, as illustrated (Fig. 1 E, G ).

Female (Fig. 8 B, C ): As male unless otherwise stated (Fig. 1 B, D, F, H ): colour pattern blue replaced by yellow tending to white (Fig. 8 B, C ). Posterior pronotal lobe weakly developed, smooth, without spine. Tibiae not dilated. Abdomen, full stripe on S 1, S 2–6 the basal bands extend dorsally but do not form complete rings. S 7 with on ventro-distal marking, but pale in middle; S 8 with complete pale yellow broad ventral border to tergite; S 9 broadly pale yellow ventrally, S 10 and anal appendages entirely pale (Fig. 1 H ).

This description agrees almost exactly with Hämäläinen (2003) and hence we may be confident of the identity of the larvae from which specimens were bred.

Distribution.

Lao PDR: Bolikhamsai Province, Kaew Neua Pass area ( Hämäläinen 2003, 2020); Vietnam: Nghe An Province, Yen Khe Commune, Con Cuong District (this study, new record); China: Guizhou Province, Libo County, Maolan National Nature Reserve ( Pu et al. 2019; this study); Guangxi Province, Hechi, Jinchengjiang District ( Yu 2010; Hämäläinen 2020).

Habitat and biology.

The larvae of P. phasmovolans inhabit forest pools, which are small, shallow bodies of water formed by rainwater or slow-moving streams (Fig. 9 ). These pools may be temporary or permanent. The larvae secrete themselves among riparian vegetation and leaf litter. The composition of the pool or stream bed where collections were made included silt (30 %), small stones / pebbles / gravel / sand (5 %), leaf litter (45 %), and riparian / root tree debris (20 %). The larval coloration acts as camouflage, allowing them to blend perfectly with their surroundings. Black larvae were typically found in dark-brown leaf litter mixed with silt or mud, whereas yellowish / brown larvae were found on riparian roots or brown / yellow leaf litter, such as bamboo leaves. The larvae were found coexisting with the larvae of Coeliccia spp. , Copera vittata (Selys, 1863) , and Copera marginipes (Rambur, 1842) . Adults of P. phasmovolans were also observed mating and laying eggs near the larval habitats. The larvae displayed agonistic behaviour (Fig. 10 ), characterized by the tendency to hold the distal end of the abdomen slightly upturned, while the caudal lamellae were splayed and pointed upwards.

Figures

Figure 1. Adult characters of Platycnemis phasmovolans A, C, E, G male B, D, F, H female A, B head, frontal view C, D thorax, lateral view E abdominal tip including appendages, dorsal view F posterior pronotal lobe of prothorax in lateral view G – H abdominal tip including appendages, lateral view.

Figure 2. Colour variation of Platycnemis phasmovolans larva A pale yellowish-brown B dark yellowish-brown C blackish-brown.

Figure 3. Head of Platycnemis phasmovolans larva A dorsal view B ventral view C frontal view D back view E lateral view. Arrow: prominence on occipital margin; triangle: row of spine and setae on genae.

Figure 4. Antenna and mouth parts of Platycnemis phasmovolans larva A left antenna B prementum, dorsal view C prementum, lateral view D left labial palp E detail of distal left palpal lobe F ligula (median lobe).

Figure 5. Compound eyes and mouth parts of Platycnemis phasmovolans larva A genae B left maxilla, dorsal view C left maxilla, lateral view D right mandible, ventro-internal view E right mandible, internal view F left mandible, internal view G left mandible, ventro-internal view. Arrow indicates row of spines and setae.

Figure 6. Abdomen and gonapophysis of Platycnemis phasmovolans larva A S 1–10, dorsal view B male gonapophysis, lateral view C male gonapophysis, dorsal view D female gonapophysis, lateral view E female gonapophysis, dorsal view.

Figure 7. Caudal lamellae of Platycnemis phasmovolans larva A median lamella B lateral lamella.

Figure 8. Adult habitus A male B female C immature female.

Figure 9. Habitat of Platycnemis phasmovolans larva A small spring-fed pool in forest B rainwater drainage path C pool in bamboo trunk (man-made) D seasonal forest pool

Figure 10. Platycnemis phasmovolans larva display agonistic display behaviour.