Tibial combs in the Cydnidae (Hemiptera: Heteroptera) and their functional, taxonomic and phylogenetic significance

Tibial combs in representatives of the family Cydnidae are described in detail for the first time. The structure was studied in 98 species of 58 genera representing all the subfamilies, among them 16 species were investigated using scanning electron microscopic (SEM) techniques. In addition, Parastrachia japonensis (Scott, 1880) of the family Parastrachiidae, and two species of Dismegistus Amyot and Serville, 1843 (a genus of uncertain systematic position within Pentatomoidea) have also been studied. Morphological terminology is proposed for all the structures connected with tibial combs and the term 'the tibial comb complex' is suggested; its functional, taxonomic and phylogenetic significance is also discussed. The genera of Cydnidae can be classified into two groups depending on differences in the tibial comb complex, when it is present; moreover, its absence in the tribe Scaptocorini (Cephalocteinae) is demonstrated for the first time and is regarded as an autapomorphy of this tribe. Data on the occurrence of tibial combs in other families of true bugs (Hemiptera: Heteroptera) are also briefly reviewed, and an anagenetic trend in their evolution in terrestrial Heteroptera is hypothesized. The presence of tibial combs on all legs is regarded as the most plesiomorphic state.