Non-monophyly of the "cydnoid" complex within Pentatomoidea (Hemiptera: Heteroptera) revealed by Bayesian phylogenetic analysis of nuclear rDNA sequences

The “cydnoid” complex of pentatomoid families, including Cydnidae, Parastrachiidae, Thaumastellidae, and Thyreocoridae, is morphologically defined by the presence of an array of more or less flattened stout setae (called coxal combs), situated on the distal margin of coxae. These structures, suggested to prevent the coxal-trochanteral articulation from injuries caused by particles of soil, sand or dust, by their nature and function are unknown elsewhere in the Heteroptera. As such, coxal combs were regarded as a synapomorphy of this group of families, and enabled the definition of it as a monophylum. In this study, the monophyly of the “cydnoid” complex of families is tested for the first time, based on the combined analysis of nuclear ribosomal DNA sequences (28S rDNA D3 region, and 18S rDNA). Combined analyses of both genes are performed using Bayesian methods with the covarion option in MrBayes 3.2.0. Non-monophyly of the entire “cydnoid” complex of families, and independent origins of their coxal combs is suggested. The family Thaumastellidae is demonstrated not to be part of this complex as previously proposed. Challenging the existing classification system, the use of the name “cydnoid” complex is indicated as unwarranted, and therefore it should no longer be applied to this group of families.