Fine structure of the ommatidia of the short-faced scorpionfly Panorpodes kuandianensis (Mecoptera: Panorpodidae).

The fine structure of the ommatidia in males of the short-faced scorpionfly Panorpodes kuandianensis was investigated using scanning and transmission electron microscopy. The result shows that the compound eyes of male P. kuandianensis are of the apposition type, consisting of over 1700 ommatidia. Each ommatidium is composed of a laminated cornea, a eucone crystalline cone, eight retinula cells, a pair of primary pigment cells, and a group of 16 secondary pigment cells. Along the optical axis of the ommatidium, seven elongated retinula cells contribute their rhabdomeres to a centrally fused rhabdom, which is in tight contact with the proximal end of the crystalline cone, but smaller than the cone end in diameter. The eighth retinula cell is located above the basal lamina and only contributes its rhabdomere to the proximal part of the rhabdom. The microvilli of the rhabdom show an orthogonally-arranged orientation. The ommatidia of Panorpodidae are more similar to those of Panorpidae than Bittacidae in structure, adding weight to the view that the sister group of Panorpodidae is Panorpidae rather than Bittacidae.