Micrathyria paulsoni González-Soriano, 2020

Novelo-Gutiérrez, Rodolfo & Arce-Pérez, Roberto, 2021, Description of the larva of Micrathyria paulsoni González-Soriano, 2020 (Odonata Libellulidae), Zootaxa 4981 (2), pp. 357-364 : 358-363

Micrathyria paulsoni González-Soriano, 2020

( Figs. 1–5 )

Material studied: 6 exuviae (5♂♂, 1♀, reared), 10 F-0 larvae. MEXICO: Veracruz; Xalapa, Jardín Botánico “Fracisco Javier Clavijero”, artificial pond (19° 30.744’N, 96° 56.622’W) elevation 1337 m, 20 June 1990, R. Novelo leg. , 1 exuvia; same data but 15 July 2020, R. Novelo, F. Ramírez leg. , 13 F-0 larvae, two ♂♂ emerged on 19 July 2020 at 22:50 h and 23:30 h, one ♂ emerged on 21 July 2020 at 23:45 h; same data but Huatusco, Laguna de Santo Domingo , 4 km NW of Huatusco (19° 09.550’N, 97° 00.267’W), elevation 1400 m, 9 July 2000, R. Novelo leg. , 3 F-0 larvae, one ♂ emerged on 12 July 2000, one ♀ emerged on 14 July 2000.

Description. Larvae small-sized, body yellowish-brown with a complex pattern of dark spots ( Fig. 1 ), hind legs relatively long, abdomen lacking dorsal protuberances, large posterolateral spines on S8−9, S10 annular and sunken into S9, and caudal appendages sharply pointed.

Head ( Fig. 2a ). Twice wider than long, wider than thorax, yellow, with large brown spots and dark brown transversal stripes. Labrum pale with a lateral brown spot on each side, anterior margin straight, slightly flattened ventromedially, and with abundant stiff setae. Clypeus bare, pale, with a transverse, comma-shaped, brown stripe on each side of midline. Antefrons dark brown, postfrons pale with four brown spots and a central inverted “u”-shaped stripe ( Fig. 2a ), anterior margin slightly convex with a row of spaced, minute, white, delicate setae. Antennae 7-segmented ( Fig. 2a ), scape and pedicel barrel-shaped, flagellomeres cylindrical and subequal in length, antennomeres 6−7 longest; scape and pedicel yellow, antennomere 3 basal half pale, distal half light brown, antennomeres 4, 5, and 7 yellow, antennomere 6 mostly dark brown with both ends pale; size proportions: 0.3, 0.45, 0.8, 0.6, 0.8, 1.0, 1.0. Vertex pale ( Fig. 2a ), shallowly convex, a transverse, jagged, dark-brown stripe between anterior and posterior ocelli, another transverse, widely open V-shaped, dark-brown stripe behind posterior ocelli, parallel to the ecdysial line. Compound eyes rounded, strongly prominent laterally ( Figs. 1a , 2a ). Occiput yellow with large irregular brown spots, covered with short, stout, spiniform setae and long bristle-like setae mainly on posterior and lateral margins; lateral margins short, more or less straight and convergent posteriorly, posterior corners widely rounded; posterior occipital margin straight. Mandibles ( Figs. 3a, b ) without molar crest, with formula: L 1234 0 abb’/ R 1234 y ab+b’d, b>a>b’ in left mandible b>d>a in right mandible; both mandibles with a large, dark, laterobasal spot. Maxilla ( Fig. 3c ): galeolacinia with seven teeth, three dorsal teeth of which the two apical teeth are moderately incurved and similar length, but basal one almost straight and shorter, four ventral teeth of different sizes and robustness, basal tooth shortest, apical one largest, maxillary palp a little shorter than galeolacinia, ending in a robust blunt spine, both galeolacinia and palp with abundant, long, robust setae. Ventral pad of hypopharynx transversally enlarged, anterior margin convex with abundant long setae, posterior margin concave with a row of stiff setae directed apically. Labium ( Figs. 4a–c ): Prementum-postmentum articulation reaches anterior margin of mesocoxae ( Fig. 1b ). Prementum subpentagonal ( Fig. 4a ), as long as the widest part, lateral margins smooth, widely concave, and divergent apically; large premental setae 9–10 ( Fig. 4a ), additional smaller setae 4−5 on each side of midline; a row of 2–3 short spiniform setae at the base of palp articulation; ligula well-developed ( Figs. 4a, b ), anterior margin finely serrulate with the medial apex convex, sides straight, a submarginal row of 7−8 stout spiniform setae to each side of tip, tip with 2–3 spiniform setae, if 3 then middle one shorter. Labial palpi strongly developed, covering inferior part of face as a mask, each with 7–8 poorly developed (obsolete) crenations on apical margin ( Fig. 4c ), each crenation finely serrulate with a graduate series of 3–4 stout setae per crenation, ventral seta largest ( Fig. 4c ); 10 palpal setae on dorsal margin ( Figs. 4a, c ), ventral margin in dorsal and ventral views appearing almost straight ( Figs. 4a, b ), in mesal view strongly convex ( Fig. 4c ), serrulate, with a row of 13–15 setae of which 10–11 out of them are longer and robust setae; external surface of palp with a subapical, ventral, dark, diffuse, irregular spot ( Fig. 4b ), internal surface with 6–7 small spiniform setae close to palpal base; movable hook long and slender, little longer than contiguous seta, sharply pointed and smooth. Ventral surface of prementum light yellow ( Fig. 4b ) covered with sparse delicate setae and minute spiniform setae.

Thorax. Prothorax ( Fig. 2a ) narrower than head. Pronotal disc pale with a wide, dark brown, longitudinal stripe on each side of a pale, narrow middorsal stripe; anterior margin shallowly concave with a row of short spiniform setae; posterior margin sinuate, widely convex at middle; sides rounded and beset with rows of short, stout, spiniform setae and a row of long stiff setae. Proepisternum anterior margin hirsute ( Fig. 2a ). Pterothorax pale with brown irregular stripes and a granular appearance ( Fig. 1a ). Legs pale with three dark bands on femora and tibiae ( Fig. 1a ), those on metatibiae very diffuse, setose, and relatively long (i.e. when fully extended, hind tibia almost reaches the tip of paraprocts); femora with dorsal and ventral rows of stout spiniform setae and some long bristle-like setae; tibiae with rows of long, stout, stiff, reddish-brown, bristle-like setae mainly on dorsal margins; tri- and tetradentate setae on distal fourth of ventral (internal) surface of tibiae and on ventromesal row of tarsi; pretarsal claws simple with a pulvilliform empodium. Wing sheaths parallel ( Fig. 1a ), pale, with longitudinal dark brown stripes; anterior and posterior wing sheaths surpass anterior margin and basal half of S6, respectively. Mesosternum anterolateral margins convex and beset with a tuft of stiff stout setae ( Fig. 1b ). Poststernite anterior margin very short, narrowly rounded, its width 0.14x the poststernite midline length ( Fig. 1b ).

Abdomen ( Figs. 1 , 2b ). Widest at S6–7 and abruptly truncate posteriorly. Terga creamy-pale on middle third of S2–5, lateral thirds yellow with dark brown dots; S6–9 yellow with abundant dark brown dots and a wide, dark brown, longitudinal stripe on each side of a pale, middorsal, longitudinal, narrow stripe, and some sparse, long, dark reddish-brown, bristle-like setae. Posterior margins of S2–9, lateral margins of S5–9, and dorsal surface of S6–9 covered abundantly with small spiniform setae, which increase in size and robustness posteriorly and intermingled with long, dark, stiff, bristle-like setae on S8–9. Middorsal protuberances lacking. Posterolateral spines large and sharply pointed on S8–9 ( Figs. 1a , 2b ), those on S8 half the middorsal length of the segment; spines on S9 as long as or little longer the middorsal length of the segment. S10 very short and sunken into S9. Sternum creamy-pale ( Fig. 1b ), S5–9 with a brown irregular brown spot on each laterosternite which increase in size and darkness posteriorly, medial sternites with dark brown dots and spots which increase in abundance posteriorly. Posterior margins of sterna 1–6 smooth, 7–9 with a row of small spiniform setae, largest on 9. Sterna 4–9 with long, dark, bristle-like setae increasing in size, number, and darkness posteriorly, forming two transversal rows on sternite 9, one subapical and another one apical. Sterna 3–5 and 8–9 each divided into five sternites and sterna 6–7 into three sternites, the anterior laterosternite on S8 very small, best visible in exuviae. Caudal appendages long, thick, and sharply pointed ( Figs. 2b , 4d ). Epiproct triangular, 0.10x longer than its basal width, yellow with a large, dark brown lateral spot on basal half, in lateral view ( Fig. 4d ) basal half shallowly concave, tip slightly decurved, lateral margins with a row of long, black, stiff, bristle-like setae and 1–2 large, subapical, middorsal, stout spiniform setae. Paraprocts dark brown laterally ( Fig. 4d ), yellow mesally, pyramidal, 0.40x longer than epiproct, dorsal and ventral margins beset with rows of stout, spiniform setae and black bristle-like setae, tips long, slender, and straight. Cerci mostly yellow ( Fig. 4d ), digitiform, shortest, 0.20x shorter than epiproct, and tips straight.

Measurements [averages in brackets, N=9]. TL 14.7–17.0 [16.3]; AL (ventral) 9.6–10.9 [10.2]; MWa 4.5–5.8 [5.0]; MWh 4.7–4.9 [4.8]; HfL (lateral) 4.0–4.5 [4.3]; Ep 1.0; Pp 1.6–1.8 [1.64]; Ce 0.6–0.7 [0.66]; spine on S8 0.3–0.5 [0.4], on S9 0.6–0.8 [0.67].

Diagnosis. González-Soriano (2020) stated that M. paulsoni belongs in the “ Micrathyria didyma ” group which also includes M. hypodidyma Calvert, 1906 , M. laevigata Calvert, 1909 , M. pseudhypodidyma Costa, Lourenço & Viera, 2002 , M. sympriona Tennessen, 2000 , and M. venezuelae De Marmels, 1989 . Of these, only the larvae of M. didyma and M. hypodidyma have been described ( Needham 1943, Santos 1968). The larva of M. paulsoni can be separated from that of M. didyma as follows (features of M. didyma in parentheses): TL ≤ 17mm (18mm, sometimes much smaller [ Tennessen 2019]), long stout setae on occiput yellow [dark brown], palpal setae 10 (12), a graduate series of 3–4 stout setae on each poorly developed palp crenation, [two stout setae, one very large]. The larvae of M. hypodidyma and M. paulsoni appear very similar in the number of premental setae (9–10 long setae plus 3–4 or 4–5 short setae) and palpal setae (10). However, some differences can be established judging by the figures provided by Santos (1968) [features of M. hypodidyma in brackets]: M. paulsoni has 2–3 setae on ligula’s tip and 7–8 spiniform setae to each side of it [two setae on ligula’s tip and a row of six setae to each side of it]; S7 lacking posterolateral spine [a small posterolateral spine on S7]; the pair of submedian dark spots on S6–9 are larger, subquadrate, and wider than the intervening pale space [subrectangular dark spots on S5–9, pale space between them on each segment 4x the width of each submedian spot]; epiproct apical third with 1–2 dorsal stout setae [two stout setae]; TL ≤ 17 mm [19 mm]. Finally, both species are far separated geografically.

Habitat. The larvae of M. paulsoni were collected in a small natural lagoon in the cloud forest with abundant vegetation around it in the vicinity of Huatusco, as well as in two contiguous artificial ponds in Xalapa ( Fig. 5 ). The artificial ponds were shallow, densely covered by floating Salvinia sp. (Salviniaceae) and submerged Najas sp. (Najadaceae) ; one pond had a large patch of floating Eichhornia sp. (Pontederiaceae) . Larvae probably cling to stems of the abundant Najas sp.

Figures

FIGURE 1. Micrathyria paulsoni, habitus F-0 larva. a) Dorsal, b) ventral.

FIGURE 2. Micrathyria paulsoni details of larval morphology. a) Head and pronotum, dorsal view; b) S5−10, dorsal.

FIGURE 3. Micrathyria paulsoni details of larval morphology. a) Right mandible, ventrointernal view; b) left mandible, internal view; c) right maxilla, mesal view.

FIGURE 4. Micrathyria paulsoni details of larval morphology. a) Prementum, dorsal view; b) ídem, ventral view; c) right labial palp, mesal view; d) S7−10 and caudal appendages, lateral view.

FIGURE 5. Micrathyria paulsoni larval habitat. Artificial ponds densely covered by Salvinia sp. (Salviniaceae) and Najas sp. (Najadaceae), Xalapa, Veracruz.