Macrothemis 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 : 243-244

Key to the fourteen known ultimate stadium larvae of Macrothemis Hagen, 1868

Keys to Macrothemis larvae were published in Ramírez & Novelo-Gutiérrez (1999), Heckman (2006) and Costa et al. (2010). The latter includes the 10 larvae described so far, but unfortunately does not allow correct identification of those species: observation errors were detected (couplet 5); equivocal steps (couplet 6, where the outputs to steps 7 and 8 are certainly changed); characters considering structures difficult to visualize and define (couplets 1 and 7); and characters variable individually and ill-defined (couplets 3, 4, 8 and 9). Moreover, with the adoption of only one character in most of the couplets, larvae not keyed from undescribed species of the genus or relatives can be easily wrongly identified without the chance to raise any suspicion. Therefore, we tried to avoid the problems listed above in the present key, using at least two characters in each step. Nevertheless, taking into account the problems inherent in the definition of the genus and the low number of larvae known (14 of 42 species), it must be used with extreme caution since there is no key that allows unambiguously identifying any given larva to Macrothemis . Attempting to minimize this problem, the first couplets were constructed to separate the known larvae of Macrothemis from those of allied genera.

1. Cuticle of abdominal terga mostly setose (covered with hair-like setae); cercus generally longer than half of epiproct... 2

1’. Cuticle of abdominal terga mostly granulose (covered with peg-like setae); cercus generally shorter than half of epiproct........................................................................... Brechmorhoga and Scapanea

2 (1). Row of premental setae arranged in one group; palpal setella generally distinct; distal margin of labial palp with cylindrical setae; lateral spine of S9 straight................................................ 5 ( Macrothemis type larvae)

2’. Row of premental setae divided in two groups, the external with two setae; palpal setella indistinct; distal margin of labial palp with flattened setae; lateral spine of S9 curved inward............................ 3 ( Gynothemis type larvae)

3 (2’). Head width distinctly greater than 1/3 of total length of larva; premental setae 8................................. 4

3’. Head width approximately 1/3 of total length of larva; premental setae generally 6 or 7, if 8 the outer margin of palpus has only 3 short flat setae...................................................................... Gynothemis

4 (3). Labial palp with five palpal setae; epiproct longer than paraproct in lateral view..................... M. heteronycha

4’. Labial palp with four palpal setae; epiproct shorter than paraproct..................................... M. musiva

5 (2). Ligula moderately prominent, with lateral margins forming an angle>90o ( Fig. 15 ); antennomeres 5–7 each distinctly lon- ger than half of 3................................................................................... 6

5’. Ligula very prominent, with lateral margins forming an angle <90o ( Fig. 34 ); antennomeres 5–7 each distinctly shorter than half of 3................................................................................... M. tenuis

6 (5). Labial palp with crenations semicircular, notches deep (typical crenations) ( Figs. 13–14 ); dorsal hook of S9 shorter and less or equally pronounced distally than corresponding lateral spine in dorsal view............................... 7

6’. Labial palp with obsolete crenations ( Figs. 32–33 ); dorsal hook of S9 distinctly longer and more pronounced distally than corresponding lateral spine in dorsal view....................................................... M. hahneli

7 (6). Dorsal hook of S5 not reduced, similar to or larger than those of preceding segments; dorsal hooks present on S6–9.... 8

7’. Dorsal hook of S5 reduced, distinctly smaller than those of preceding segments; dorsal hooks absent on S6– 9 M. meurgeyi

8 (7). Dorsal hook on S2, sometimes very small, tubercle-like ( Figs. 16–17 ); 10–12 premental setae...................... 9

8’. Dorsal hook absent on S2 ( Figs. 7–8 ); 7–10 premental setae................................................ 12

9 (8). Labial palp with 6 palpal setae; total length> 15.5 mm .................................................... 10

9’. Labial palp with 7 palpal setae; total length ca 13 mm .......................................... M. inequiunguis

10 (9). Dorsal hooks of S7–9 similar to those of preceding segments and with acute apex; apex of lateral spine of S9 distally reaching 0.66 of epiproct length in dorsal view (S10 and caudal appendages distinctly embedded in S9)............. 11

10’. Dorsal hooks of S7–9 distinctly smaller than those of preceding segments and with blunt apex; apex of lateral spine of S9 reaching distal border of S 10 in dorsal view (S10 and caudal appendages weakly embedded in S9)..... M. aurimaculata

11 (10). Dorsal hook of S2 shorter than the mediodorsal length of the segment; dorsal hooks of S6–7 similar to those of other segments, hook-like.......................................................................... M. declivata

11’. Dorsal hook of S2 subequal to or larger than the mediodorsal length of segment; dorsal hooks of S6–7 less pronounced than those of other segments, spine-like … M. ultima

12 (8’). Labial palp with 6–7 palpal setae; ligula with lateral margins forming an angle of 110–130o....................... 13

12’. Labial palp with 5 palpal setae; ligula with lateral margins forming an angle of ca. 100o............... M. hemichlora

13 (12). Movable hook of labial palp stout, its midlength thickness at least 3x thicker than the preceding palpal seta; apex of lateral spine of S9 distally reaching the level of apex of paraproct in dorsal view (S10 and caudal appendages very embedded in S9)............................................................................................. 14

13’. Movable hook of labial palp slender, its midlength thickness ≤ 2x as thick as the preceding palpal seta; apex of lateral spine of S9 distally reaching at maximum 0.66 of epiproct length in dorsal view (S10 and caudal appendages moderately embedded in S9)....................................................................................... 15

14 (13). Lateral margins of ligula forming an angle of ca. 110o; dorsal hooks of S8–9 notably smaller than those of S5–7................................................................................................. M. celeno

14’. Lateral margins of ligula forming an angle of ca. 125o; dorsal hooks of S8–9 similar to those of S5–7........ M. inacuta

15 (13’). Row of premental setae with an internal group of 3–4 smaller setae; labial palp with 8–9 crenations... M. imitans imitans

15’. Row of premental setae with an internal group of 2, exceptionally 3, smaller setae; labial palp with 7, exceptionally 8, crenations............................................................................... M. pseudimitans

Figures

FIGURES 11 – 20. Macrothemis declivata Calvert, 1909, ultimate stadium larva, 3: 11. right mandible, inner view; 12. left mandible, inner view; 13. right labial palp, dorsal view; 14. distal border of right labial palp, ventral view; 15. prementum, dorsal view; 16. abdomen, dorsal view; 17. abdomen, lateral view; 18. abdominal segment 9, ventral view; 19 caudal appendages, dorsal view; 20. caudal appendages, lateral view.

FIGURES 30 – 38. Macrothemis tenuis Hagen, 1868, ultimate stadium larva, 3: 30. right mandible, inner view; 31. left mandible, inner view; 32. right labial palp, dorsal view; 33. distal border of right labial palp, ventral view; 34. prementum, dorsal view; 35. abdomen, dorsal view; 36. abdomen, lateral view; 37. caudal appendages, dorsal view; 38. caudal appendages, lateral view.

FIGURES 1 – 10. Macrothemis imitans imitans Karsch, 1890, ultimate stadium larva, 3: 1 head, dorsal view; 2. right mandible, inner view; 3. left mandible, inner view; 4. right labial palp, dorsal view; 5. distal border of right labial palp, ventral view; 6. prementum, dorsal view; 7. abdomen, dorsal view; 8. abdomen, lateral view; 9. caudal appendages, dorsal view; 10. caudal appendages, lateral view. “ a ” and “ b ”, measurements used to represent the projection of ligula.