Evidence from other orders, from the thorax, and from fossils supports the pleural, not tergal, origin of the abdominal lateral sclerites, including the heteropterous connexivum. A plesiomorphic pregenital abdominal segment thus consists of a dorsal tergum, a ventral sternum (zygosternum), a dorsal epipleurite, and a spiracle-bearing ventral hypopleurite. The abdominal morphology supports the classification of the order Hemiptera into 4 suborders. In the suborder Sternorrhyncha, the terga and sterna are both moderately convex, and tymbals are absent. The infraorder Psyllomorpha retain only the spiracle-bearing hypopleurites, whereas in the Aphidomorpha, both the dorsal epipleurites and ventral hypopleurites are visible in the more sclerotized forms; a distinct pleurite bears spiracle 1. In the suborder Auchenorrhyncha, the terga are usually large and strongly arched, the sterna relatively small and flattened, and tymbals are usually present. The pleurites are ventralized so that the terga form the lateral margin of the abdomen, and the hypopleurites infold. In the infraorder Cicadomorpha, spiracles 3–6 are on hypopleurites and spiracles 2 and 7 on epipleurites except in the Cicadelloidea (sensu lato), in which spiracle 3 is on an epipleurite. In the Fulgoromorpha, the spiracles are on epipleurites and the hypopleurites are often reduced, a trend culminating in the Delphacidae, which have only 1 set of pleurites. The fulgoroid abdominal sterna have distinct groups of trichobothria, which appear homologous with the trichobothria of the trichophorous Pentatomomorpha and the Peloridiidae. The suborder Coleorrhyncha have flat terga, large convex sterna, and sharp lateral connexives. Sterna 2 and 3 are fused and sternum 2 is excavated and grooved. Spiracles 3–7 are on large ventral hypopleurites and spiracles 1 and 2 are on dorsal epipleurites. The abdominal sterna bear small scattered trichobothria. The ground plan of the suborder Heteroptera similarly has flat terga, large convex sterna, a sharp lateral connexive, but plesiomorphic dorsal epipleurites and ventral spiracle-bearing hypopleurites on segments 2–7 or 8. When present, spiracle 1 is dorsal in the membrane between the metanotum and tergum I, as in the Auchenorrhyncha. Although free in other hemipterans, terga 1 and 2 are firmly united in the Heteroptera and a distinct apodeme forms a sulcus at the line of union. Similar apodemes occur in the Coleorrhyncha on the posterior margins of terga 1 and 2. These tergal apodemes in the Heteroptera, and probably in the Coleorrhyncha, form in part Jordan’s organ, a tymbal that is vibrated more by dorsal longitudinal muscles than is the tymbal of the Auchenorrhyncha, which is vibrated more by dorsoventral muscles. Stridulatory mechanisms in the Hemiptera are probably secondary to the tymbals to provide higher pitches. The connexiva of the Leptopodomorpha and the trichophorous Pentatomomorpha are probably synapomorphous in being turned over so that the hypopleurites are dorsalized and the epipleurites infold. Because the Aradoidea have the plesiomorphic abdominal condition as compared with the Leptopodomorpha + Pentatomomorpha, it is proposed that the Aradoidea constitute a separate heteropteran infraorder, Aradomorpha, new infraorder.