Onychophora: References

Budd, G. E. (2001). Tardigrades as "stem-group arthropods": the evidence from the Cambrian fauna. Zoologischer Anzeiger, 240, 265–279. pdf
Euonychophora.

Cavalier-Smith T (August 1998). "A revised six-kingdom system of life". Biol Rev Camb Philos Soc 73 (3): 203–66. doi:10.1111/j.1469-185X.1998.tb00030.x. PMID 9809012.
Onychophora.

David A. Grimaldi, Michael S. Engel, and Paul C. Nascimbene 2002 Fossiliferous Cretaceous Amber from Myanmar (Burma): Its Rediscovery, Biotic Diversity, and Paleontological Significance pdf

Gregory D. Edgecombe, 2010 Arthropod phylogeny: An overview from the perspectives of morphology, molecular data and the fossil record. Arthropod Structure & Development 39 (2010) 74.87
Onychophora

Hoffmann, K. 1997: Ecdysteroids in Adult Females of a 'Walking Worm' Euperipatoides leuckartii (Onychophora, Peripatopsidae). Invert. Reprod. Dev. 32: 27-30.
Euonychophora.

Hou, Xianguang; Bergström, J. 1995: Cambrian Lobopodians - Ancestors of Extant Onychophorans. Zoological Journal of the Linnaean Society 114: 3-19.
Onychophora

Jacobs, David K.; Wray, Charles G.; Wedeen, Cathy J.; Kostriken, Richard; DeSalle, Rob; Staton, Joseph L.; Gates, Ruth D.; Lindberg, David R. 2000: Molluscan engrailed Expression, Serial Organization, and Shell Evolution. Evolution & Development, vol. 2 (6): 340-347.
Onychophora.

Nielsen, C. (2001). Animal Evolution: Interrelationships of the Living Phyla, Second Edition. 563 pp. Oxford University Press.
Euonychophora, Onychophora.

Qiang Ou, Jianni Liu, Degan Shu, Jian Han, Zhifei Zhang, Xiaoqiao Wan, and Qianping Lei, 2011 A Rare Onychophoran-Like Lobopodian from the Lower Cambrian Chengjiang Lagerstätte, Southwestern China, and its Phylogenetic Implications Journal of Paleontology, 85(3):587-594. DOI: 10.1666/09-147R2.1 pdf
Antennacanthopodia, Onychophora

Thompson, I. and Jones, D. 1980: A Possible Onychophoran from the Middle Pennsylvanian Mazon Creek beds of Northern Illinois. Journal of Paleontology 54: 588-596.
Helenodora.