Mystrocneme sectum is a species of moth in the subfamily Arctiinae (tiger moths) within the family Erebidae. It was first described by the British entomologist William James Kaye in 1911. The species is found in Guyana (formerly British Guiana), with the type locality recorded as the Potaro River region.
The moth is characterized by a black thorax with a large central metallic-green spot and additional metallic-green spots on the patagia and collar. It has a white frons and shoulder spot, metallic-green lateral stripes on the abdomen with a white sublateral basal spot, and black forewings featuring a small marking. Its wingspan is approximately 28 mm.
The species belongs to the genus Mystrocneme, a small Neotropical genus of tiger moths established by Gottlieb August Wilhelm Herrich-Schäffer in 1855. The genus comprises four known species: Mystrocneme albicorpus, Mystrocneme atavia, Mystrocneme sectum, and Mystrocneme varipes, all primarily distributed across northern South America.
