Epigomphus sulcatistyla Donnelly, 1989

Novelo-Gutiérrez, Rodolfo & Gómez-Anaya, José Antonio, 2024, The rediscovery of Epigomphus sulcatistyla Donnelly, 1989, with a description of its larva and female (Odonata: Gomphidae), Zootaxa 5446 (1), pp. 133-142 : 134-141

Larva description of Epigomphus sulcatistyla Donnelly

( Figs. 1–3 )

Material. Eight exuviae (4 ♂♂, 4 ♀♀, reared), 8 young larvae. MEXICO: Veracruz; Municipality of San Andrés Tuxtla, Estación de Biología Tropical “Los Tuxtlas”, UNAM, stream elev. 102 m (18°29.193 N, 95°04.896 W), 17 April 2023, 2 F-0 larvae (emerged 23 May 2023 at 13:15 h (♀) and 24 May 2023 (♂ )); Municipality of Catemaco, Dos Amates, stream elev. 351 m (18°25.622 N, 95°04.995 W), 17 April 2023, one F-0 larva (♂ emerged 1 June 2023 at 11:50 h); same data but km 7.1 road Tebanca-Miguel Hidalgo , stream elev. 402 (18°15.349 N, 94°57.516 W), 4 October 2022, 8 young larvae; same data but km 8.4 road Tebanca-Miguel Hidalgo , stream elev. 507 (18°18.335 N, 94°59.253 W), 18 April 2023, 5 F-0 larvae (2 ♂♂, 3♀♀, all emerged between May 27 and June 03); all specimens J.A. Gómez, R. Novelo leg.

Description. Medium-size exuviae (25.8–30.0 mm total length), body robust, antennae, legs and sides of thorax setose, gently tapering caudad, body light yellow-brown lacking any particular pattern ( Figs. 1 a-b), young larvae light yellow with a dark brown, complex color pattern on abdomen ( Fig. 1c ).

Head: Wider than long, wider than prothorax but narrower than pterothorax and abdomen ( Fig. 1 ). Labrum mostly bare, anterior border with dense brush of golden setae, flattened ventrally; anteclypeus bare, postclypeus, frons, vertex and occiput with minute, moderately abundant scale-like setae, a tuft of long, upturned, golden setae on anterolateral margins of frons (between antenna and anterior margin of compound eye), occiput mostly bare, each occipital lobe with two large, circular, bare areas and with long, golden setae on lateral margins. Anterior margin of frons shallowly concave. Antennae 4-segmented ( Fig. 2a ), covered with minute, scale-like setae dorsally, and dense rows of long, yellowish setae on lateral margins, those on external margins longest, those on internal margins stiff, scape globose, pedicel subglobose, 3 rd antennomere largest, spindle-shaped, flattened dorsoventrally, almost twice as long as widest part, 4 th antennomere a small blunt cone; scape, pedicel and 3 rd antennomere yellow-brown, 4 th antennomere reddish brown, size proportions: 0.30, 0.20, 1.0, 0.10. Compound eyes moderately developed; ocelli pale. Occipital lobes rounded, bulging; a well-developed longitudinal carina beset with small, stiff setae to each side of ventral surface of head. Mandibles ( Figs. 3 a-d) with molar crest, formula: L 1234 -y a(m 1,2,3)b / R 1234 y a(m 1,2,3)b, in both mandibles tooth a>b. Maxillae: galeolacinia ( Figs. 3 e-f) with 7 moderately incurved teeth, three dorsal teeth more or less of same length and robustness, four ventral teeth of different size, apical one largest; maxillary palp thick and robust. Ventral pad of hypopharynx pentagonal, whitish, soft, with a row of ventral, subapical, long, stiff setae, basal margin concave, sclerotized. Labium: prementum-postmentum articulation reaching posterior margin of procoxae ( Fig. 2b ). Prementum reddish brown, subrectangular, slightly longer than its widest part, lateral margins smooth, slightly sinuate, convex at apical 0.50, convergent on basal 0.37, basal margin shallowly concave ( Fig. 2b ); without a longitudinal, central sulcus on ventral surface, a small, shallow, concavity just below ligula beset with some long setae; ligula poorly developed ( Fig. 2c ), W/L ratio 1:0.20, apical margin slightly convex, with a ventral row of 8 (88 %) to 10 (12 %) reddish brown, short, truncate teeth on middle, a dorsal row of long, whitish piliform setae, and a middle row of short, stout, brown setae; labial palp stout ( Fig. 2c ), reddish brown, mostly glabrous, with some sparse, long, delicate setae on external surface; apical lobe stout, tip rounded and finely scalloped, internal margin almost straight with 10–11 small, truncate teeth, external margin gently convex and smooth; movable hook reddish-brown, shorter than palp, sharp and moderately incurved.

Thorax: Prothorax slightly narrower than head ( Fig. 1a ), setose on inferior border. Anterior margin of pronotum slightly concave, lateral margins convex and bulging, posterior margin convex; a large, subquadrate glabrous area on each side of midline, remainder of pronotum with sparse, minute, scale-like setae. Pterothorax mostly bare, with minute, sparse, scale-like setae and some tufts of long, curled setae on inferior margins, mesospiracles well-developed, metaspiracles reduced. Legs short ( Fig. 1 ) (when fully extended, hind legs scarcely reaching posterior margin of S7), strongly setose, with long, yellow-brown, delicate setae mainly on sides and shorter, stiff, reddish setae mainly on anterior surfaces of tibiae and tarsi; burrowing hooks moderately developed ( Figs. 1 , 2b ); dorsal margins of metafemora same length as metatibiae ( Fig. 1a ); tarsal formula 2-2-3, claws simple, with a pulvilliform empodium, metatarsal claws yellow-brown on basal 0.75, distal 0.25 reddish-brown. Wing sheaths scarcely surpassing anterior margin of S4, strongly divergent ( Fig. 1a ), mostly bare, with sparse, minute scale-like setae, and abundant long, delicate setae on borders.

Abdomen: Yellow-brown, with a complex pattern of dark and pale areas only visible in larvae not exuviae ( Fig. 1c ), more or less spindle-shaped, ventral surface flat, dorsal surface convex, lacking dorsal protuberances, widest on S5; lateral margins of S1–9 with long, stiff yellowish setae, with scale-like setae on S10, lateral margins of S8–9 serrate, serrations stout and sharp, S7–9 ending in slightly upturned, sharply pointed spines increasing in size and robustness posteriorly, those of S7–8 slightly divergent ( Fig. 2d ); tergites 2–10 with combined short and long, delicate setae mainly on dorsolateral thirds and also with minute scale-like setae, all of them sparse except on posterior margins where scale-like setae are abundant; tergites 3–8 with a thin, longitudinal, middle suture. Sternites following same color pattern as tergites; sternites 3–8 divided into five plates, sternites 2 and 9 divided into three plates, ventral sutures parallel on 2–3, diverging gradually on 4–8, strongly divergent on 9. Male gonapophyses lacking, with evident circular gonopore ( Fig. 1b ); female gonapophyses vestigial, roundly-pointed, slightly divergent distally ( Fig. 2e ). Caudal appendages ( Figs. 1 , 2d ) dark reddish brown, pyramidal, sharplypointed, with abundant setae on internal margins, with scale-like setae on external margins of cerci and paraprocts, external margins concave, tips of cerci and paraprocts more or less parallel, paraprocts and cerci subequal, epiproct slightly longer; male epiproct with a pair of bare dorsal tubercles along basal 0.50, rounded apically and divergent distally ( Fig. 2d ).

Measurements [in mm, averages in brackets]: Exuviae (N = 7): TL 25.8–30.0 [27.8]; AL (ventral, excl. caudal app.) 15–17 [16.2]; MWh 5.8–6.5 [6.1]; HfL (lateral) 5.0–5.2 [5.1]; MWa (ventral) 6.8–8.0 [7.3]; Ep 1.1–1.5 [1.4], Ce 1.1–1.4 [1.3], Pp 1.1–1.4 [1.3]; spine on S7 0.2-0.3 [0.2], spine on S8 0.4-0.5 [0.4], spine on S9 0.6-0.8 [0.7].

Habitat. Larvae were found in small, shallow streams of 2nd and 3rd order, at sluggish margins in shady places, inhabiting banks of fine sand, mud and leaf litter.

Female description

( Fig. 4 )

The following description is based upon four teneral females reared from F-0 larvae.

Head: Labrum grayish, ventrolateral margins black, distal margin fringed with dark brown, bristle-like setae, some scattered bristle-like setae on surface to each side of midline ( Fig. 4a ); sides of mandibles and genae creamy pale; anteclypeus distally grayish, yellow basally, postclypeus light brown, wider than anteclypeus with the anterior corners, rounded, bulging, and with marginal, black, bristle-like setae ( Fig. 4a ); antefrons light brown, postfrons shallowly concave at middle, with a large, pale spot to each side of midline and with scattered, black, bristle-like setae ( Figs. 4a–b ); vertex brown, distally striated, ocelli yellow, with a low, mound-like tubercle behind each lateral ocellus ( Fig. 4b ). Compound eyes grayish-yellow ( Figs. 4a–b ) (pale grayish-blue when alive). Occiput mostly yellowish-brown, brown at sides, striated on anterior half ( Fig. 4b ), with a large concavity to each side of midline ( Figs. 4b–c ), posterior margin sinuose, concave at middle ( Fig. 4b ), with a small, subglobose, tubercle at each side ( Fig. 4b ). Rear of head light brown, a large ear-like pit on postgenae (sensu Calvert 1920) ( Fig. 4c ), each pit with a mesal and lateral ridge, the mesal ridge followed by vertical, well-marked, impressed striae ( Figs. 4b–c ).

Thorax: Prothorax pale brown ( Fig. 4d ), middle lobe pale at sides with paired yellow mesal spots on the posterior margin; posterior lobe brown. Pterothorax pale brown above, pale below ( Figs. 4d–e ), yellow stripes as follows: 1 st antehumeral stripe not connected to pale anterior collar ( Fig. 4e ), 2 nd antehumeral stripe thin, wider at anterior end reaching the yellow mesokatepisternum ( Fig. 4e ); mesepimeral stripe subequal in width throughout, reaching the subalar carina; metepisternal stripe wide, narrowing gradually posteriorly not reaching the subalar carina and connected anteriorly with the yellow metakatepisternum; metepisternum mostly light yellow; metasternum pale ( Fig. 4e ); antealar crest and sinuses pale brown, pale laterally. Legs ( Fig. 4e ): coxae yellow, trochanter and basal half of femora grayish, tibiae brownish-black, tarsi and spines armature black. Wing venation black, pterostigmata grayish-yellow.

Abdomen: Dorsally brown, laterally pale on S1, S2 with a full-length pale stripe, S3 with a pale stripe on basal 0.80, S4–6 with a pale ring on basal 0.33, S7 with basal half pale, S8–10 light brown with some irregular yellow spots ( Fig. 4f ), S10 yellow laterally ( Fig. 4g ). Caudal appendages ( Figs. 4f–g ): epiproct light brown with posterior margin black, distally roundly-pointed; cerci reddish-brown, acutely-pointed, the longest, 4.8x as long as its maximum width; paraprocts yellowish-brown, with dorsal borders creamy pale, roundly-pointed, the shortest. Vulvar lamina ( Fig. 4h ) widely U-shaped, reaching basal half of sternum 9, with tips strongly divergent, each branch comprising 0.75 of vulvar lamina total length.

Measurements (in mm): AL 38–39; HwL 41–42.

Figures

FIGURE 1. Epigomphus sulcatistyla: a) last stadium male exuvia, dorsal view; b) Ídem, ventral view; c) Young larva showing the complex abdominal color pattern, dorsal view.

FIGURE 2. Epigomphus sulcatistyla: a) antennae of a young larva, dorsal view; b) prementum of the last stadium exuvia, ventral view; c) detail of the palps and ligula, ventral view; d) S7–10 and caudal appendages of male, dorsal view; e) sterna 9–10 of the female showing the vestigial gonapophyses.

FIGURE 3. Details of the mouthparts of the last stadium exuvia of Epigomphus sulcatistyla: a–d) mandibles: a–b, right mandible, ventral and mesal view, respectively; c–d, left mandible, ventro-mesal and mesal view, respectively; e–f) left maxilla, ventral and mesal view, respectively.

FIGURE 4. Details of the morphology of the female imago of Epgomphus sulcatistyla: a–c) head: frontal, dorsal, and posterior views, respectively; d) thorax, dorsal view; e) head and thorax, lateral view; f–h) S9–10 and caudal appendages: f) dorsal view; g) left lateral view; h) ventral view, showing the vulvar lamina.