The rhabdom structure in the ommatidia of the Heteroptera (Insecta), and its phylogenetic significance

In its plesiomorphic state the insect ommatidium consists of eight retinula cells forming a fused rhabdom. It has long been observed that, in contrast to this pattern, Heteroptera have open rhabdoms. However, there has so far been no comprehensive and comparative study of heteropteran ommatidia. For this reason, we investigated the rhabdom structure in 36 species from all higher groups of Heteroptera, as well as from Coleorrhyncha and Auchenorrhy ncha as outgroup representatives. In addition we surveyed the data of earli er authors, which brings the number of examined species to a total of more than 70. All examined Heteroptera do have open rhabdoms, with a system of s ix peripheral and two central rhabdomeres. Outgroup comparison shows that t he open rhabdom is an autapomorphy of the Heteroptera. As for the rhabdom s tructure within the Heteroptera, we found further autapomorphic patterns in Corixidae (Nepomorpha), Gerromorpha, and Leptopodomorpha. Finally, the Cim icomorpha and Pentatomomorpha share a special pattern of the two central rh abdomeres, which we call V-pattern. This is a new synapomorphy of these two taxa.