As far as the approach to cladistic relationships among infraorders
of the Heteroptera is concerned, several various hypotheses have been proposed with respect to the systematic position of the Nepomorpha as well as other infraorders
(generally without considering the Aradimorpha) and discussed in phylogenetic studies.
An updated checklist of decapod crustaceans (infraorders
Astacidea, Thalassinidea, Polychelidae, Palinura and Anomura) from the northern and northeastern Brazilian coast.
(1993), mainly in that Psylloidea is the sister group of Heteropterodea, Sternorrhyncha and Cicadomorpha are paraphyletic, and in the internal relationships of the Heteroptera infraorders
(Leptopodomorpha, Cimicomorpha, and Pentatomomorpha are in a polytomy, Enicocephalomorpha is the sister group of this clade, and the remaining infraorders
forms a basal group in an unresolved polytomy).
Mice, rats, hamsters, squirrels, and gerbils are classified in the other rodent Suborder Sciurognathi, which is divisible into Infraorders
Sciuromorpha (squirrel-like rodents) and Myomorpha (mice and rats; Luckett and Hartenberger 1985).
Silks were collected from spiders in the infraorders
Mygalomorphae and Araneomorphae.
From these findings, it is assumed that some decapod sub- and infraorders
evolved independently to exploit different peptidase catalytic mechanisms, including the use of serine, cysteine, and aspartic peptidases for hydrolysis of peptide bonds in food proteins, the evolution forces leading to such variable digestive mechanisms remain unknown.
In comparison with the other heteropteran infraorders
it has been observed that the morphology and distribution of the labial tip sensilla in the Nepomorpha are distinctly varied with respect to what has been reported in the Gerromorpha (Brozek and Zettel, in prep), Pentatomomorpha [19, 21], and Cimicomorpha: Reduviidae [15, 25].
Monophyly of Gerromorpha has been confirmed by later studies (e.g., Damgaard, 2008b), whereas relationships with other infraorders
remain disputed (Wheeler et al., 1993; Mahner, 1993; Shcherbakov and Popov, 2002; Xie et al., 2008).
Ceratocombomorpha, composed of the families Ceratocombidae, Hypsipterigidae, and Schizopteridae, is an additional infraorder
to the 7 infraorders
recognized at present in Heteroptera.
Given that the giant escape circuit is absent in representative species in both Palinuridae (this study) and Scyllaridae (Faulkes, 2004), it is more parsimonious to assume that the giant escape circuit was lost once in the palinuran infraorders
rather than repeatedly throughout the group.