Triacanthagyna dentata (Geijskes, 1943)

DeMarmels, Jurg, 1992, Dragonflies (Odonata) From The Sierras Of Tapirapeco And Unturan, In The Extreme South Of Venezuela, Acta Biologica Venezuelica 14 (1), pp. 57-78 : 65

Triacanthagyna dentata (Geijskes, 1943)

Figures 49-50 (adult); 51-57 (larva)

Material. 2♀ (reared, with their exuviae), Base Camp.

Female. The two females correspond fairly well with the description of the male type given b:y Geijskes (1943). In one female the triangles in left fore and right hind wing have two proximal longitudinal veins each. In the other female the cos· tao subcosta and pterostigma of the left fore wing are completely unpigmented (white). Ovipositor short; central pronge of threepronged ventral process on abdominal segment 10 more than twice the length of lateral pronges. Anal appendages dark brown, as long as segments 8, 9 and 10 together ( Figs. 49-50 ).

Measurements. Total length (excl. appendages) 59-66; abdomen (excl. app.) 44-50; anal appendages 7-8; hind wing 49-50.5; pterostigma (costal side, front wing) 4.4-4.8; same (hind wing) 3.3-4.0.

Larva. Brown, without definite pattern of longitudinal lines on abdominal dorsum. A dark area under lateral angle of prothoracic hind lobe and a rounded dark spot above middle coxa, on the mesepimeron. Antennae seven-jointed; occipital lobes not bulging laterally, with their outer margins converging towards occiput, the latter slightly concave ( Fig. 51 ). Labium ( Fig. 52 ) reaching backwards to middle coxae; two long palpal setae close to base of movable hook, and a third one slightly more proximally ( Fig. 53 ). In one specimen the left lateral palp lacks the proximal seta. Hind border of pronotum gently rounded, the lateral angles produced into a pointed triangle. First projection of prothoracic supracoxal process spine-shaped, the second triangularly pointed ( Fig. 54 ). Femora with two dark cross-bands and dark tip; dark cross-bands of tibiae largely fused and pale areas reduced to one or two ill-defined spots. Wing sheaths not reaching to end of segment 4, each with two dark comma-shaped dashes in the central area. Abdomen with lateral spines on segments 5-9, but those of segment 5 extremely small ( Fig. 55 ). All anal appendages of about the same length and as long as segments 9+10 together; epiproct truncated ( Fig. 56 ); gonapophyses reaching backwards slightly into segment 10 ( Fig. 57 ).

Measurements. Total length 38.0; greatest width of head across compound eyes 8.0; hind femur 6.2;hind tibia 6.7.

Remarks. This is the first record of T. dentata from Venezuela. Adults were not seen. but in numerous phytotelmata held by a fallen tree (see under Microstigma rotundatum ) about a dozen larvae of early instars were found, together with also small larvae of Libellula herculea Karsch. Only the two females could be brought to emergence.

Santos (1973) describes the larva of T. caribbea Williamson, and Carvalho (1988) that of T. ditzleri Williamson. From both, T. dentata larvae might be separated on the basis of the reduced number and peculiar disposition of the palpal setae.

Figures

Plate VI: Figures 47-48. Aeshna c. planaltica, male ultimate instar exuviae, (47) labium, ventral view; (48) anal pyramid, dorsal view. Figures 49-57. Triacanthagyna dentata, female. (49) tipo of abdomen (adult) with anal appendages, left lateral view; (50) same, dorsal view; (51) head (ultimate instar exuviae), dorsal view; (52) labium, ventral view; (53) apical portion of labium with right palp, dorsal view; (54) right prothoracic supracoxal process, dorsal view; (55) part of abdomen showing left lateral spines, dorsal view; (56) anal pyramid, dorsal view; (57) abdominal segment 9 with gonapophyses, ventral view.