Idiocnemis mertoni

Idiocnemis mertoni is a medium-sized dark-colored damselfly distinguished by its contrasting purple and black thoracic coloration and strongly curved male anal appendages. The head resembles that of I. bidentata, with a diffuse semi-rectangular black marking surrounding the ocelli, while the frons and vertex around it are entirely metallic purple. Thorax predominantly dark brown to black with a broad purple antehumeral stripe covering most of the mesepisternum, a feature more extensive than in related species. The underside of the synthorax is characteristically dark brown to black with a sharply delimited white posterior area. Wings hyaline with a medium-brown pterostigma. The abdomen is slender with distinct purple dorsal markings on segments 1–5 and again on segments 8–9, while segment 7 remains mostly dark brown. Male superior anal appendages yellow to yellow-brown and strongly curved, representing one of the most diagnostic characters of the species; inferior appendages about two-thirds the length of the superiors. Females are recognized by the uniquely shaped posterior pronotal lobe, consisting of a blunt median triangle flanked by two lateral hooks. Idiocnemis mertoni differs from closely related I. dagnyae by its broader purple thoracic markings, darker ventral synthorax with sharply contrasting white posterior area, black antennal scapus, and especially the strongly curved superior appendages and distinctive female pronotal lobe morphology.