Cryptophaea vietnamensis ( van Tol & Rozendaal, 1995 )

Phan, Quoc Toan & Keetapithchayakul, Tosaphol Saetung, 2024, Description of the final stadium larva of Cryptophaea vietnamensis (van Tol & Rozendaal, 1995) (Odonata: Euphaeidae) from Vietnam, Zootaxa 5512 (1), pp. 93-102 : 94-101

Description of larva of Cryptophaea vietnamensis ( van Tol & Rozendaal, 1995)

Material examined. VIETNAM. 3 exuviae: 1 ♂, 1 ♀ (last stadium larvae when collected, then reared in laboratory), 1 ♀ (exuviae collected from sampling site), Bach Ma National Park (16°07’07.3”N 107°59’02.3”E, elevation 1314 m a.s.l.), Thua Thien-Hue province, 7/IV/2024, Q.T. Phan & T.S. Keetapithchayakul leg.

2 last stadium larvae: 1 ♂ Dak Glei (15° 12’ 04.4” N, 107° 44’ 02.3” E, elevation 1083 m a.s.l.), Kon Tum province, 29/II/2024, Q.T. Phan & T.S. Keetapithchayakul leg. , 1 ♀, (16°07’07.3”N 107°59’02.3”E, elevation 1314 m a.s.l.), Bach Ma National Park , Thua Thien-Hue province, 19/IV/2024, T.S. Keetapithchayakul leg.

Description of larva based on 1 ♂ (exuvia) and 1 ♀ (F–1).

Habitus ( Fig. 1 ) stout but moderately elongate, long robust legs with broad flattened femora, abdomen semi– cylindrical, tapered caudad, with seven pairs of ventral gills on S2–8, caudal gills elongate-saccoid with blunt and pale tips, brownish to brownish-black.

Head: strongly flattened, broad and pentagonal in shape; maximum width / length ratio of ca 1.51 ( Fig. 2A ). Antennae ( Fig. 2B ), long, 1.19 times as long as distance from central hind margin of head to base of labrum, 7-segmented, with A3 longest, relative length of antennomeres 0.59: 0.89: 1: 0.81: 0.59: 0.28: 0.09, A1–7 with scattered small SS, and A1 and A2 with scattered CVS. Labrum ( Fig. 2C ) flattened ventrally, outline with convex corners flanking central anterior concavity, fringed with long SS distally and scattered CVS on basal half, the longest distinctly curved; clypeus rather bulbous, antefrons with scattered small SS and CVS; vertex with 3 prominent ocelli; compound eyes broad and rounded, slightly protruding antero-laterally; postocular lobes almost rounded in outline and scattered CVS and SPS, so that posterior margin of head is deeply convex, with a narrow flange at posterior occipital margin, fitting closely to anterior dome of prothorax ( Figs 1 , 2A ). In dorsal view ( Fig. 2A ) outer part of mandibles, anterior angles of prementum, and labial palps all extending beyond labrum and visible. Genae ( Fig. 2D ) with row of 20–24 short blunt spines arranged in a line below eye margin; interspersed with long SS and CVS along ventral margin of compound eyes. Articulation of labial prementum and postmentum reaching level of anterior of mid coxa. Prementum ( Fig. 3A ) wedge-shaped with distinctly sinuous, laterodistal margin with 5–6 small CVS, lateral margins bearing well-defined denticles (25–28 small spines) each spine bearing SS, for 2/3 their length ( Fig. 3B ); maximum width wider than 0.73 length, with a pair of SS on middle of ventro-posterior side in ventral view; ligula (median lobe) ( Fig. 3C ) strongly produced, distinct convex lobes forming bifid profile with finely serrate margin; tiny median cleft, extending to a pigmented elongate trace; one pair of small tubercles between median cleft and 1–2 pair of SS, scattered small SS. Lobe of labial palp ( Fig. 3D ) 0.35 of length of prementum, outer margin with row of spines (each spine bearing small SS) from near base to midpoint, inner margin with narrow flange transversely grooved and weakly serrated in distal 3/4, palpal lobe apically trifid ( Fig. 3E ); outer process with moderately uncinate flattened process with a wavy outer margin, middle lobe longest and thicker, terminally rounded weakly uncinate tooth; inner lobe securiform with tiny teeth; movable hook strong and short about 0.67 time as long as labial palp, tapered to acute apex, curving moderately inwards. Mandible ( Fig. 4A–F ) with mandibular formula: L 1+1’234 0 a(m 1,2,3,4)b / R 1+1’234 y a(m 0)b, asymmetrical, four incisors, well developed, 4>3>2>1>1’, molar crest with six teeth (a>1=2>4=b>3) on left mandible; two teeth (a>b) on the right mandible. Outer margin of mandible smoothly angulate without obvious spines, bearing antero-laterally long CVS and SS. Maxilla ( Fig. 4G–H ) galeolacinia with 7 teeth, 4 dorsal teeth of approximately the same size, apical teeth largest, 3 ventral teeth of small size.

Thorax: Prothorax trapezoidal, narrower than head, with scattered CVS intermingled with SS, antero-lateral view with 7–9 spines protruding laterally ( Fig. 5A ); posterior margin rounded, with row of CVS; wing pads almost parallel, fore- and hindwing pads reaching base of middle of S4 and anterior margins of S5 respectively. Legs with femora especially broad and flattened, covered with dense SS, intermingled with SLS and CVS, forecoxae with tuft of CVS ( Fig. 5A ); tibial comb ( Fig. 5B ) with numerous SS intermingled with SLS and CVS in dorsal view, with numerous SS locating distal margin end in ventral view; tarsi with 2 rows of SS and scattered long simple setae.

Abdomen: narrowing caudally; scattered SLS, intermingled with CVS and SS; abdominal terga, with a row of SLS and SS on posterior margin, abdominal terga S3–9 with a cluster of long SS on the middle of posterior margin; abdominal pleura scattered SLS; abdominal sterna smooth, seven pairs of tapered abdominal gills on S2–8 becoming progressively shorter and more slender posteriorly. Male gonapophyses ( Fig. 6A–B ) well developed, base stout, tips blunt; almost semicircular in lateral view with serrate ventral margin formed by acute, broad-based, raised triangular plates; slightly divergent distally in ventral view, reaching posterior margin of S10; gonopore small, embossed O-shaped with central fissure; female gonapophyses ( Fig. 6C–D ) comprising 2 pairs of long valves, with lateral valves slightly arching from anterior margin of abdominal sternite S8, with acute, broad-based, with TWS on base, raised triangular plates raised triangular plates with CVS on the ventral side; tips rounded, extending well beyond abdominal sternite S10; central valves smooth, slender, apically rounded, and longer than lateral valves. Caudal gills ( Figs 1 , 6E ) large, saccoid, uniformly elongate with well-defined midrib then tapering gradually, with stout and short filament; everywhere with dense SS, posteriorly with sparse SLS and SS, median gill very similar to lateral gills.

Measurements: (in mm; n = 5 (2 F-1 alcohol preserved specimens and 3 exuviae)—Minimum–Maximum [mean]: total length of body without caudal gills = 13.59–15.10 [14.42]; length of caudal gills (median: lateral) = 6.41: 6.49; width and length of head = 2.46–3.01 [2.76] and 2.70–2.97 [2.87]; length of antenna = 2.74–2.84 [2.80]; maximum width and length of prementum = 2.57–2.76 [2.70] and 3.47–3.71 [3.59]; length of inner and outer wing pads = 5.29–5.62 [5.40] and 4.95–5.21 [5.05]; length of femora (fore: mid: hind) = 2.38–2.69 [2.49]: 2.74–3.04 [2.93]: 3.46–4.08 [3.86]; length of tibiae (fore: mid: hind) = 2.76–3.04 [2.93]: 2.64–3.02 [2.82]: 3.17–3.90 [3.60].

Habitat and biology

The larvae of C. vietnamensis inhabit small streams in dense upland primary forest. The composition of the stream bed where collections were made was as follows: pebble/gravel/sand/silt (30%), small stones (40%), leaf litter (10%), aquatic plants (5%), large rocks (10%), and boulders (5%). The larvae clung to the substrate, often upside down, under stones in slow riffles and sometimes were found together with larvae of Anisopleura Selys, 1853 , Bayadera and Euphaea Selys, 1840 . Their exuviae were found on large rocks and boulders. C. vietnamensis is distributed in the northern part of the Central Highlands, Vietnam. Oviposition by adults was observed, with the females laying their eggs directly into the bark of tree trunks (20–30 cm above water surface) unguarded by their mates ( Fig. 7 ).

Discussion

The discovery of C. vietnamensis larvae has raised the number of euphaeid genera for which larvae of some species are known to seven out of nine genera, adding to two recent additions ( Nguyen et al. 2024; Orr & Hämäläinen 2024). The larva of Cryptophaea bear a strong resemblance to Bayadera , with which they may co-occur. The two genera share characters such as short and blunt tipped saccoid gills, deep posterior cephalic lobes without sinuous posterior margin ( Fig. 2A ), relatively long antennae and wavy outer edge of the outer lobe of the labial palp ( Fig. 3E ), unknown in other genera; the male genital apophyses are also similarly and uniquely hypertrophied. The main differences between C. vietnamensis and known Bayadera species are twofold –– the distal margin of ligula is more produced in C. vietnamensis with a distinctly bilobed convex margin ( Fig. 3C ) (while smoothly convex in Bayadera , for instance, see fig. 4d in Keetapithchayakul et al. 2020; fig. 4d in Yang & Orr 2024) and poorly developed spines on outer margin of mandible ( Fig. 4A, E ) (but well developed in Bayadera for which this character is known; except for B. ishigakiana Asahina, 1964 ) (see fig. 249 in Ishida (1996); fig. 5b, c in Keetapithchayakul et al. (2020); fig. 4f, h in Yang and Orr (2024)). Information on these characteristics is available in only about half of Bayadera species for which the larva has been described, as both older and recent literature often lack details, resulting in uncertainty about the diagnostic importance of various characters. It is however clear that C. vietnamensis is most nearly related to Bayadera and larvae of the two taxa differ considerably from other euphaeid genera (see Keetapithchayakul et al. 2020; Keetapithchayakul et al. 2024; Yang & Orr 2024; Nguyen et al. 2024; Orr & Hämäläinen 2024).

At present for the family Euphaeidae only the two monotypic genera, Cyclophaea and Schmidtiphaea remain undescribed in the larval stage; these were classified as a vulnerable species with decreasing population and data deficient, respectively ( Dow 2020a, b). Both are also species with small ranges, and S. schmidi Asahina, 1978 is seriously data deficient (zero records in iNaturalist (2024)); both occur in at-risk habitats, making it a priority to locate their larvae, which may offer valuable insights into their taxonomic relationships. Moreover, the understanding of larval habitat requirements could contribute significantly to conservation efforts.

Figures

FIGURE 1. Larval habitus of final stadium Cryptophaea vietnamensis.

FIGURE 2. Detail of antenna, head, frons, labrum, and genae of Cryptophaea vietnamensis: (A), head, dorsal view; (B), right antenna; (C), frons and labrum, antero-dorsal view; (D), left genae, ventral view.

FIGURE 3. Detail of labium of Cryptophaea vietnamensis: (A), prementum and labial palps, dorsal view; (B), detail showing dentate lateral margin of prementum;(C), ligulawith median cleft, dorsal view; (D), right labial palp, dorsal view; (E) enlargement of distal end of palpal lobe.

FIGURE 4. Detail of mandibles and maxillae of Cryptophaea vietnamensis: (A–C) right mandible: (A), lateral view; (B), ventrointernal view; (C), inner view; (D–F) left mandible: (D), ventrointernal view; (E), lateral view; (F) inner view; (G), distal part of left galeolacinia and palp, ventral view; (H), detail of left galeolacinia, internal view.

FIGURE 5. Detail of prothorax and distal part of leg of Cryptophaea vietnamensis: (A), prothorax with procoxa, dorsal view; (B), tip of fore tibia and tarsi, ventral view.

FIGURE 6. Detail of S8–10 and caudal gill of Cryptophaea vietnamensis: (A–B) male: (A), lateral view; (B), ventral view; (C–D) female: (C), lateral view; (D), ventral view; (E) caudal gill, dorsal view.

FIGURE 7. Female of Cryptophaea vietnamensis ovipositing: eggs are laid directly into the bark of a tree trunk.