Progomphus joergenseni Ris, 1908

Muzón, Javier & Lozano, Federico, 2011, Description of the final instar larva of Progomphus joergenseni Ris (Epiprocta: Gomphidae), Zootaxa 2762 (1), pp. 56-60 : 57

Progomphus joergenseni Ris

Description of the last instar larva

Figures 1–2

Head. Antenna ( Fig. 1b ): third segment elongated, fringed with long setae, fourth segment vestigial, knob-like. Mandibular formula: L 1234 0 a (m 1,2,3,4) b/ R 1234 y a+b; molar crests very different from each other, the teeth on the left mandible are assembled in two groups (those on the anterior margin more irregular; Fig. 1f ), whereas the right one has two teeth, a (rounded) and b (sharply pointed), which are fused at their bases forming a crest without intermediate teeth ( Fig. 1g ). Prementum ( Fig. 1d ) 1.2 times as long as wide, reaching front margin of second coxae, slightly wider anteriorly; ligula fringed with short and long setae and with a pair of minute dark denticles medially ( Fig. 1e ); labial palp ( Fig. 1c ) with inner margin crenulated, distal tooth as long as 1.2 times the length of the outer margin.

Thorax. Pronotum: posterior 0.7 laterally expanded with convex margins. Front and middle legs not fossorial, but tibiae with burrowing hooks. Tarsal claws symmetrical. Ratio of the distance between pro, meso and metacoxae 1.2: 1: 2.

Abdomen. Pale, dark pattern as follows: two dark dorsal spots on S5–8, cerci and male genital opercula ( Fig. 1a ). Widest at S6, quickly tapering beyond middle segments; S9 as long as 0.82 times S8 and 1.38 times length of S10; dorsal hooks ( Fig. 2a ) on S2–9, those on S2–3 the biggest; lateral spines ( Fig. 2b ) on S6–9, ratio between spine length and middorsal length of corresponding segment 0.11 / 0.26 / 0.32 / 0.32. Ventral longitudinal sutures on S2–9. Paraprocts: inner ventral margin straight, as long as 2.48 times S10 middorsal length; paraproct to epiproct and cerci ratio: 1: 0.94: 0.45.

Measurements (in mm): n = 7 (4 larvae, 3 exuviae). Total length 27.5–30.0. Head maximun width (only larvae) 5.1–5.3; antena 3 rd segment 1.35–1.10; labium maximun width 2.9–2.5; labium maximun length 3.3–2.8; labial palp length 0.6–0.9; labial palp movable hook length 0.8–1.0. Inner wingpad length 6.25–5.7; distance between 3rd coxae 1.96–2.12; fémur I length 2.2–2.4; femur II 2.38–2.76; femur III 3.71–4.30; tibia III 3.5–3.07. Dorsal length of S5 1.12 –1.44, S6 1.10 –1.47, S7 1.12 –1.40, S8 1.06 –1.28, S9 0.89 –1.02, S10 0.60 –0.73. Cercus length 0.70– 0.80; paraprocts 1.79–1.50; epiproct 1.50–1.69.

Diagnosis. Typical (according to Belle 1991, 1992 and Needham 1941) Progomphus medium size larvae. The last instar larva of P. joergenseni can be easily distinguished from P. complicatus (characters between parentheses) by the vestigial and knob like fourth antennal segment (elongated) a pair of denticles in ligula (denticles absent) and the regular claws (cheliform). On the other hand, the last instar larva of P. phyllocromus and P. lepidus is very similar to P. joergenseni , differing only in the size of dorsal hooks on S5–9 (smaller in P. phyllochromus and P. lepidus ).

In Patagonia the other gomphid genus recorded is Neogomphus Selys ; apart from the fact that Progomphus was recorded only in arid areas and Neogomphus in forest streams ( Muzón, 2009), their larvae can be easily separated by orientation of the wingpads: widely divergent in Progomphus and parallel in Neogomphus .

Figures

FIGURE 1. Progomphus joergenseni. (a) General view (dorsal view); (b) Antenna (dorsal view); (c) Labial palp (inner view); (d) Prementum (dorsal view); (e) Ligula; (f) Left mandible (inner view); (g) Right mandible (inner view); (h) Right mandible (lateral view).

FIGURE 2. Progomphus joergenseni. (a) Abdomen (lateral view); (b) Abdomen (left half, dorsal view); (c) ♂ terminalia (dorsal view); (d) ♂ terminalia (lateral view); (e) ♀ terminalia (dorsal view); (f) ♀ terminalia (lateral view).