Pancrustacea is a clade, comprising all crustaceans and hexapods. This grouping is contrary to the Atelocerata hypothesis, in which Myriapoda and Hexapoda are sister taxa, and Crustacea are only more distantly related. As of 2010, the Pancrustacea taxon is considered well accepted. The clade has also been called Tetraconata, referring to the square ommatidia of many of its members. That name is preferred by some scientists as a means of avoiding confusion with the use of "pan-" to indicate a clade that includes a crown group and all of its stem group representatives.
A monophyletic Pancrustacea has been supported by several molecular studies, in most of which the subphylum Crustacea is paraphyletic with regard to insects (that is, that insects are derived from crustacean ancestors).
In 2005 study of nuclear genomes Regier et al. suggest that Hexapoda is most closely related to Branchiopoda and Cephalocarida + Remipedia, thereby hexapods are "terrestrial crustaceans", thus confirming Pancrustacea hypothesis; and maxillopods are not monophyletic (in the following cladograms Maxillopoda subclasses are highlighted). In addition, there appeared some evidence against the Ostracoda monophyly: that Ostracoda subclass Podocopa may form a clade with Branchiura.
In 2012 molecular study von Reumont et al. challenge the monophyly of Vericrustacea: they present four versions of Pancrustacea cladogram (figures 1—4), and in all four figures Remipedia is a sister group to Hexapoda, and Branchiopoda is a sister group to (Remipedia + Hexapoda). Thus, theirs data strongly suggest that Branchiopoda more closely related to Hexapoda and Remipedia than to Multicrustacea. Based on these data, they propose the following scenario of evolution of Branchiopoda, Remipedia and Hexapoda: under the impact of predatory fishes theirs common ancestors go to the littoral zone, then ancestors of Branchiopoda go to the ephemeral freshwater habitat, whereas ancestors of Remipedia go to the Anchialine cave, and ancestors of Hexapoda go to the land.
In 2013 combined study of morphology, including fossils, and molecular data, including expressed sequence tag, mitochondrial genome, nuclear genome, and ribosomal DNA data Oakley et al. obtained support for three pancrustacean clades: Oligostraca (Ostracoda, Mystacocarida, Branchiura, Pentastomida), Multicrustacea (Copepoda, Thecostraca, Malacostraca) and a clade they refer to as Allotriocarida (Branchiopoda, Cephalocarida, Remipedia, Hexapoda), as well as for monophyly of Ostracoda. Within Multicrustacea they obtained support for a clade they suggest the name Hexanauplia: Thecostraca + Copepoda. Relations within Allotriocarida remain uncertain: sister taxon to Hexapoda is either Remipedia, or the clade Branchiopoda + Cephalocarida, however, authors are inclined to the first version (see "Conclusion", 4), which is also consistent with von Reumont et al. (2012) results.
According Petrunina A.S. and Kolbasov G.A., the sixth subclass of Maxillopoda Tantulocarida may lie within Thecostraca, forming a clade with thecostracan infraclass Cirripedia (if so, Thecostraca excluding Tantulocarida is paraphyletic):
^W. Dohle (2001). "Are the insects terrestrial crustaceans? A discussion of some new facts and arguments and the proposal of the proper name 'Tetraconata' for the monophyletic unit Crustacea+Hexapoda". Annales de la Société Entomologique de France37 (1–2): 85–103.
^ abcJerome C. Regier, Jeffrey W. Shultz, Andreas Zwick, April Hussey, Bernard Ball, Regina Wetzer, Joel W. Martin & Clifford W. Cunningham (2010). "Arthropod relationships revealed by phylogenomic analysis of nuclear protein-coding sequences". Nature463 (7284): 1079–1083. doi:10.1038/nature08742. PMID20147900.
^Casey W. Dunn, Andreas Hejnol, David Q. Matus, Kevin Pang, William E. Browne, Stephen A. Smith, Elaine Seaver, Greg W. Rouse, Matthias Obst, Gregory D. Edgecombe, Martin V. Sørensen, Steven H. D. Haddock, Andreas Schmidt-Rhaesa, Akiko Okusu, Reinhardt Møbjerg Kristensen, Ward C. Wheeler, Mark Q. Martindale & Gonzalo Giribet (2008). "Broad phylogenomic sampling improves resolution of the animal tree of life". Nature452 (10): 745–749. doi:10.1038/nature06614. PMID18322464.
^ abcdeBjoern M. von Reumont, Ronald A. Jenner, Matthew A. Wills, Emiliano Dell'Ampio, Günther Pass, Ingo Ebersberger, Benjamin Meyer, Stefan Koenemann, Thomas M. Iliffe, Alexandros Stamatakis, Oliver Niehuis, Karen Meusemann & Bernhard Misof (2012). "Pancrustacean phylogeny in the light of new phylogenomic data: support for Remipedia as the possible sister group of Hexapoda". Molecular Biology and Evolution29 (3): 1031–1045. doi:10.1093/molbev/msr270. PMID22049065.