Macrothemis tenuis Hagen, 1868

Salgado, Luiz Gustavo Vargas, Carvalho, Alcimar Do Lago & Pinto, Ângelo Parise, 2013, Larval taxonomy of Macrothemis Hagen, 1868 (Odonata: Libellulidae), with descriptions of four larvae and a key to the fourteen known species, Zootaxa 3599 (3), pp. 229-245 : 238-241

publication ID 10.11646/zootaxa.3599.3.2

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Macrothemis tenuis Hagen, 1868


Macrothemis tenuis Hagen, 1868 View in CoL

( Figures 30–38 View FIGURES 30 – 38 , 41 View FIGURES 39 – 42 )

Material. BRAZIL, Rio de Janeiro State: Itatiaia municipality, [district of] Maringá, Rio Preto (roots and litter) [22o19’37.73’’S, 44o34’41.36’’W; 1,107 m a.s.l.], 17.IX.1996, Equipe Entomologia UFRJ leg., 2 ̩ F-0 and 2 Ƥ F- 0, emergence dates unknown. All in DZRJ.

Larva similar to M. imitans imitans described above, differing by the following features: Integument without setae especially long or concentrated.

Head ( Figs. 30–34 View FIGURES 30 – 38 ). About 1.5x as wide as long in dorsal view; occipital lobes covered with short spiniform and robust long filiform setae. Frons with a group of short spiniform setae between antennae. Occiput bearing short robust setae. Proportional length of antennomeres: 30, 60, 100, 40, 35, 35, 35. Mandibular formula L 1234 y- abb’ R 1234 y abd or abdd’ ( Figs. 30–31 View FIGURES 30 – 38 ); left mandible: molars and incisors with obtuse apex, size b+d>a or dd’>a, size 3>4>1>2, prominence 3>4>1>2, y- poorly developed obtuse; right mandible: a and b with acute apex, d or dd’ and incisors with obtuse apex, size d>b>a or dd’>b>a, size 4>1>3>2, prominence 4>1>3>2, y with obtuse apex. Labium when folded reaching the level between pro- and mesocoxae; Prementum longer than wide in ventral view ( Fig. 32 View FIGURES 30 – 38 ); ligula projected 0.4, forming an angle of about 85º; margin of ligula bearing setae with truncate apex, 10 of these distinctly larger. Labial palp with 6 palpal setae ( Fig. 33 View FIGURES 30 – 38 ); proximal portion with setella and a group of 6–10 short spiniform setae; proximal half of outer margin with a row of about 6–8 short and robust setae; distal margin with 11 obsolete crenations (almost straight) ( Fig. 34 View FIGURES 30 – 38 ); central crenations with 5–7 setae, 3–4 in those closest to outer margin; setae of crenations truncate; inner margin with a row of about 25 setae.

Thorax. Pronotum with short setae; central area with a pair of nipple-like processes with rounded base; posterolateral margins with expansions with concentrations of short claviform setae; inverted “V” spot distinct both in exuviae and larvae. Prothoracic pleural processes with acute apex directed forward with a group of long and short spiniform setae. Legs with few robust setae; femora with row of short and robust setae concentrated in anterior surface; metathoracic femora when directed posteriorly reach posterior limit of S5 tergite; metatibiae when flexed on femora reaching distally the level of proximal half of trochanter; tibiae and tarsi of 3 pairs with 2 parallels rows of simple setae ventrally, extended to the distal middle of tibiae to the third segment of tarsi.

Abdomen ( Figs. 35–38 View FIGURES 30 – 38 ). About 2x longer than maximum width (S6); dorsal hooks on S2–9 large and with obtuse apex, S2 tubercle-like ( Figs. 35–36 View FIGURES 30 – 38 ); tergites with concentrations of spiniform setae on lateral margins decreasing in size gradually toward apex of abdomen; posterior borders of tergites of S1–5 bearing filiform short setae regularly distributed, those of S5 short and robust with obtuse apex in their 0.17 of lateral extension; posterior borders of tergites of S6–9 with short and robust setae with obtuse apex and S10 with few spiniform setae; lateral spines on S8–9, as long as 0.27 and 0.45 median dorsal length of respective segment; posterior border of sternum of S9 without a row of filiform long setae. Paraprocts with long, thin setae laterally.

Measurements (in mm; n=4). Total length 17.73–19.09; head mediodorsal length 2.17–3.34; head max. width 4.67–4.96; antenna total length 1.22–1.55; length of antennomeres 0.13–0.22, 0.20–0.29, 0.33–0.43, 0.15–0.19, 0.15–0.17, 0.13–0.19, 0.15–0.22; prementum length 3.91–4.44; prementum max. width 3.21–4.00; hind wing sheath length 4.75–5.42; metafemur length 4.67–5.50; metatibia length 5.30–5.96; abdomen length (incl. appendages) 7.57–8.75; abdomen max. width (S6) 4.90–5.69; epiproct length in lateral view 0.87–1.02; paraproct max. length in lateral view 0.65–0.80; cercus length in lateral view 0.61–0.71.

Diagnosis. The F-0 larva of M. tenuis cannot be correctly identified as Macrothemis in all the keys examined ( Tables 1–2), being wrongly identified as Dythemis in the majority of them, but also as Brechmorhoga ( Costa et al. 2004) and Gynothemis ( Carvalho et al. 2002) . The main feature that approximates this species, as well as M. hahneli , to those of Dythemis is the distal border of the labial palps with distinctly obsolete crenulations, a character not exclusive of this genus. However, it can be easily distinguished from all Dythemis larvae by the shape of its dorsal hooks ( Dythemis features in brackets): present on S2, tubercle-like [absent]; large and with obtuse apex [large or short but with acute apex] on S3–9 ( Figs. 35–36 View FIGURES 30 – 38 ). The following combination of characters will separate it from the other described Macrothemis larvae: antennomeres 5–7 distinctly shorter than half of 3; left mandible with tooth y reduced; ligula very prominent, with lateral margins forming an angle of ca. 85o ( Fig. 34 View FIGURES 30 – 38 ); rows of premental setae not clearly divided in two groups; crenations of distal margin of labial palps obsolete; setae of distal margin of labial palps cylindrical; lateral spines of S9 straight; dorsal hooks on S2–9 large and with obtuse apex, S2 tubercle-like ( Figs. 35–36 View FIGURES 30 – 38 ).













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