Ultrastructural diversity of compound eyes in Fulgoromorpha (Hemiptera): evidence for convergent and divergent...

The external morphology and ultrastructure of the compound eyes in adults of eight species of planthoppers were studied using scanning (SEM) and transmission (TEM) electron microscopy. The eyes are of the apposition type, and each ommatidium includes a laminated corneal lens, a crystalline cone, eight retinula cells, two primary pigment cells, 5-8 secondary pigment cells, and a basal lamina. Two distinct retinula cell patterns were observed: a "7 + 1" arrangement in studied specimens of Delphacidae and Tropiduchidae, and a "6 + 1 + 1" arrangement in those of Cixiidae, Meenoplidae, Fulgoridae, Ricaniidae, Flatidae, and Dictyopharidae. These structural differences are not consistently associated with taxonomic groupings and may reflect independent evolutionary developments. In particular, the "7 + 1" configuration in Tropiduchidae may have evolved independently from that in Delphacidae. At this stage, the ultrastructure of compound eyes exhibits unexpected and intriguing morphological variations; however, additional studies are necessary to fully capture the diversity of this ancient group before any attempt can be made to interpret these features in a phylogenetic context.