Macrothemis imitans subsp. imitans Karsch 1890

Macrothemis imitans imitans Karsch, 1890

(Figures 1–10, 39)

Material. BRAZIL, Minas Gerais State: Juiz de Fora municipality, Barrio Floresta [21o45’14.39’’S, 43o16’57.85’’W; 632 m a.s.l.], 06.II.1987, A. L. Carvalho leg., 2 ̩ F-0, adult emergences 15.II.1987 (87021-Bd), 25.II.1987 (87021- Bl) and 3 Ƥ F-0, adult emergences 09.II.1987 (87021-Ba), 13.II.1987 (87021-Bb), 14.II.1987 (87021-Bc); Rio de Janeiro State: [Comendador Levy Gasparian municipality], Mont serrat [village of Montserrat], Rio Paraibuna [22o01’08.87’’S, 43o18’37.48’’W; 365 m a.s.l.], 18–19.XI.2000, N. Ferreira-Jr. leg., ̩ F-0, emergence date unknown. All in DZRJ.

Typical libellulid larva. General color ochre. Integument covered by short filiform setae equally distributed, longer and concentrated on sides of head, thorax and legs; posterior area of head and thorax without differentiated setae.

Head (Figs. 1–6). General shape trapezoidal (Fig. 1), about twice as wide as long in dorsal view; occipital margin moderately concave, with occipital lobes little pronounced, covered with short and long filiform setae. Labrum with setae turned forward in its distal fourth. Clypeus glabrous. Frons with a group of filiform and spiniform setae turned forward between antennae. Vertex covered with short spiniform and long filiform pale setae, concentrated in a pair of prominent lateral regions. Occiput as wide as maximum width of head (including compound eyes) in dorsal view, bearing long filiform setae; posterior angles rounded; dorsal region with defined glabrous areas: a central and one anterior pair, rounded, and four lateral pairs, elongated, corresponding to muscular impressions. Lateral portion of eyes moderately pronounced upward and forward. Antenna 7-jointed; relative length of antennomeres: 74, 74, 100, 56, 67, 74, 81. Mandibular formula L 1234 0 ab / R 1234 y abd (Figs. 2–3); left mandible: molars and incisors with acute apex, size b>a, size 4>3>1>2, prominence 4>1>3>2; right mandible: molars and incisors with acute apex (incisor 2 less acute), size d>b>a, size 1=4>2=3, prominence 4>3>2>1, y with acute apex, size similar to other teeth. Labium when folded reaching median level of mesocoxae. Prementum concave (Fig. 4), approximately as long as wide, enlarging from base to apex in ventral view; ventral surface with small round dark spots usually coincident with setal insertions; ligula projected 0.3, forming an angle of about 115º; anterior margin of ligula weakly serrate, bearing a submarginal row of about 50 robust setae with acute apex on dorsal surface, a dozen distinctly longer; premental setae 8–10, disposed in arch, unequal in length, the most internal smaller, growing up to the third or fourth of row, and other (laterals) distinctly longer; external margins of prementum bearing a row of approximately 20 short filiform setae. Labial palps triangular (Fig. 5), with 6–7 palpal setae slightly longer than movable hook; movable hook slender, its midlength thickness 2x as thick as the precedent palpal seta; proximal portion of palp near articulation with setella and group of 5–7 short spiniform setae; proximal half of outer margin with a row of about 10 short and robust setae; distal margin with 8–9 crenations with serrated tip, semicircular (Fig. 6); notches between crenations decrease in depth from limits with outer (dorsal) to inner (ventral) margins; central crenations with 4–5 setae, 1–4 in those closest to outer margin; setae of crenations acute, positioned submarginally on dorsal surface, organized in relation to length in each crenation, the bigger inserted more ventrally; inner margin with a row of about 20 setae; ventral surface with small dark spots, rounded, coincident with base of setae, as in prementum.

Thorax. Pronotum with spiniform setae and a pair of robust and long setae, turned upward located medially; central area without nipple-like processes; posterolateral margins rounded, with spiniform setae directed up- and backwards, especially concentrated laterally; inverted “V” spot not distinct in exuviae and poorly evident in larvae. Prothoracic pleural processes obtuse with a concentration of long and thin setae. Fore- and hindwing sheaths reaching mid length of S5 and S6, respectively. Legs with numerous long and spiniform thin setae; metathoracic legs when fully extended surpassing level of apex of caudal appendages; femora slightly flattened laterally, with row of long, thin setae concentrated on anterior surface, directed downward; metathoracic femora when directed posteriorly reach level of mid length of S6; metathoracic tibiae when fully folded reach distally base of trochanter; third segment of metathoracic tarsi similar in length to first and second segments combined; all tarsi and tibiae with 2 parallel rows of differentiated setae ventrally, one near anterior margin (anterior row) and other near posterior margin (posterior row); prothoracic pair with anterior row composed by tridentate setae distributed between distal half of tibia and second segment of tarsus and simple setae on third; meso- and metathoracic legs with anterior row composed of simple setae distributed between base of tibiae and third segment of tarsi; posterior margin of all legs with row of simple setae, almost reaching base of tibia in prothoracic legs and restricted to distal third in meso- and metathoracic legs.

Abdomen (Figs. 7–10). General shape elliptical, lateral margins convex in dorsal view; cross section approximately semicircular (Figs. 7–8); about 1.5x longer than its maximum width (S6); dorsal hooks on S3–9, large, apex acute, gradually curved along segments, directed upward on S3 and backward on S9; hooks of S7–9 surpassing distally level of posterior edge of corresponding segment (Figs. 7–8). Tergites regularly covered with short setae; spiniform setae of lateral margins increasing in size and stiffness gradually towards apex of abdomen; posterior border of S1–5 tergites bearing short and filiform setae sparsely distributed, and spiniform setae laterally on S4–5; posterior border of S6–10 tergites with spiniform setae; lateral spines on S8–9, as long as 0.5 and 0.8 median dorsal length of its respective segment; posterior limit of tergites S3–9 with a row of spiniform setae, increasing in thickness posteriorly; posterior border of S9 sternum convex, with a row of spiniform setae and a pair of lateral tufts of long, filiform setae directed posteriorly and curved inward (as in Fig. 18). Caudal appendages acute (Figs. 9–10); paraprocts pyramidal, as long as epiproct in lateral view and of S9–10 together in dorsal view; cerci conical ca. 0.66 of epiproct length in lateral view; apex of paraprocts straight; apex of epiproct and cerci obliquely curved downward in lateral view; paraprocts with some setae long and robust laterally.

Measurements (in mm; n=5). Total length 13.50–17.34; head mediodorsal length 1.65–2.82; head maximum width 3.80–5.52; antenna total length 1.35–1.44; antennomeres length 0.19–0.20, 0.19–0.21, 0.26–0.28, 0.14–0.16, 0.17–0.18, 0.17–0.19, 0.21–0.22; prementum length 2.69–4.39; prementum maximum width 2.88–3.87; hind wing sheath length 3.36–4.45; metafemur length 2.70–4.13; metatibia length 3.36–4.41; abdomen length (incl. appendages) 6.12–8.80; abdomen maximum width (S6) 4.15–5.56; epiproct length, lateral view 0.74–0.96; paraproct maximum length, lateral view 0.60–0.87; cercus length, lateral view 0.50–0.70.

Diagnosis. The F-0 larva of M. imitans imitans can be correctly identified as Macrothemis in the majority of the keys examined, except that of Rodríguez Capítulo (1992) (Tables 1–2). This species, along with M. pseudimitans, presents the more generalized morphology among the species of the genus. The following combination of characters separates these species from the other described larvae of the genus: antennomeres 5–7 longer than half of 3; ligula moderately prominent with lateral margins forming an angle of ca. 110o (Fig. 15); premental setae 8–10, not clearly divided in two groups; labial palps with “normal” crenations (semicircular, notches deep) (Figs. 13–14); palpal setae 6–7; distal margin of labial palps with cylindrical setae; movable hook slender, its midlength thickness scarcely 2x or less as thick as the preceding palpal seta; dorsal hooks on S3–9 (Figs. 7–8); dorsal hook of S5 not reduced, similar or larger than those of preceding segments; dorsal hook of S9 shorter and less pronounced distally than correspondent lateral spines in dorsal view; lateral spines of S9 straight, apex reaching at maximum the level of 0.66 of epiproct in dorsal view (S10 and caudal appendages moderately embedded in S9). The larva of Macrothemis imitans imitans can be separate from that of M. pseudimitans by only two characters, both with some level of superposition of conditions (M. pseudimitans alternative in parentheses): row of premental setae with an internal group of 3–4 (2, exceptionally 3) smaller setae; labial palps with 8–9 (7, exceptionally 8) crenations. Based on adults, Daigle (2007) considered M. imitans imitans (referred only as M. imitans) the closest relative of M. meurgeyi. However, comparing the F-0 larva of M. imitans imitans with that of M. meurgeyi (Meurgey 2009), it is easily detectable that these species are very dissimilar, as shown by the characters used in the key presented below. Mainly due to the absence of dorsal hooks on S6–9, an exceptional feature in Macrothemis, it was not possible to identify M. meurgeyi even to genus level in all the keys inspected (Tables 1–2).