THE LARVAL EYE OF NANNOCHORISTID SCORPIONFLIES (INSECTA, MECOPTERA)

The stemmata of last-instar Nannochorista larvae are compound eyes com posed of 10 or more ommatidia. Each ommatidium has four Semper cells, four distal and four proximal retinula cells which form a cruciform an d layered rhabdom. The ommatidia are separated by epidermal cells (pos sibly rudimentary pigment cells). Corneal lenses are lacking. At the p osterior edge, aberrant stemma units may be present which lack a diopt ric apparatus and have a star-shaped rhabdom composed of at least six retinula cells. The stemmata of Nannochorista appear to be derived fro m stemmata of the Panorpa-type (Mecoptera-Panorpidae). Differences bet ween the stemmata of Nannochorista and Panorpa can be explained as ada ptations to aquatic life (flat cornea) or as regression. A compound la rval eye is ascribed to the ground plan of the Mecoptera sensu lato an d is considered a genuine plesiomorphy. The identical basic number (se ven) of stemmata in the Neuropteroid/Coleoptera assemblage, Amphiesmen optera and some Mecoptera (Bittacidae, Boreidae) is attributed to para llel evolution.