Ultrastructural comparison of the compound eyes of Sinopanorpa and Panorpa (Mecoptera: Panorpidae).

The ultrastructure of the compound eyes of scorpionflies Sinopanorpa tincta (Navás, 1931), Panorpa liui Hua, 1997 and Panorpa sexspinosa Cheng, 1949 in Panorpidae were comparatively investigated using transmission electron microscopy. Their compound eyes share the following characters: each ommatidium possesses a corneal lens, a eucone tetrapartite crystalline cone surrounded by a pair of primary pigment cells, and eight retinula cells. Seven retinula cells (R1-R7) are in contact with the crystalline cone and extend to the basal lamina, but the eighth retinula cell (R8) is only restricted to the basal level of the ommatidium. The rhabdomeres of cells R1-R7 form a centrally fused rhabdom that almost spans the full length of the ommatidium, and that of R8 only contributes to the basal part of the rhabdom. The distal part of the rhabdom projects upward into the region between the cone cell tips and force the cone cells to split apart into four thin cone cell roots that run along a narrow intercellular gap between adjacent retinula cells. The number of secondary pigment cells varies from 12 in P. liui to 16 in P. sexspinosa and S. tincta. Based on the dissimilarity of the imaginal and larval ommatidial structure, the imaginal compound eyes are very unlikely to be directly developed from the larval compound eyes in the Panorpidae.