The two living families are the Peripatidae and the Peripatopsidae. They show a peculiar distribution, with the peripatids being mainly equatorial and tropical, while the peripatopsids are all found in what used to be Gondwana.
The segmented worm-like organisms have tiny eyes, antennae, multiple pairs of legs and slime glands. The group is thought to be related to arthropods. They prey on smaller animals such as insects, which they catch by squirting a sticky slime.
Possible fossil history[change | change source]
Fossils from the early Cambrian bear a striking resemblance to the velvet worms. These fossils, known as the lobopods, were marine. They were a grade from which arthropods, tardigrades, and Onychophora arose. They are found in the Cambrian, Ordovician (possibly), Silurian, and Pennsylvanian periods.
Historically, all fossil Onychophora and lobopods were lumped into the taxon Xenusia. However, few of the Cambrian fossils have features that definitely unite them with the Onychophora. The exceptions are Hallucigenia and Collinsium ciliosum, which have distinctly onychophoran-like claws.
References[change | change source]
- Piper, Ross 2007. Extraordinary animals: an encyclopedia of curious and unusual animals. Greenwood Press.
- Smith M.R. & Ortega Hernández J. 2014. "Hallucigenia’s onychophoran-like claws and the case for Tactopoda". Nature 514 (7522): 363–366. doi:10.1038/nature13576. PMID 25132546. http://rdcu.be/bKoD.
- Budd, Graham E. 2001. "Why are arthropods segmented?". Evolution & Development 3 (5): 332–42. doi:10.1046/j.1525-142X.2001.01041.x. PMID 11710765.
- Bergström, Jan; Houb, Xian-Guang (2001). "Cambrian Onychophora or Xenusians". Zoologischer Anzeiger 240 (3–4): 237–45. doi:10.1078/0044-5231-00031.
- "Ordovician faunas of Burgess Shale type". Nature 465 (7295): 215–8. doi:10.1038/nature09038. PMID 20463737.
- von Bitter, Peter H. et al 2007. "Eramosa lagerstätte—exceptionally preserved soft-bodied biotas with shallow-marine shelly and bioturbating organisms (Silurian, Ontario, Canada)". Geology 35 (10): 879–82. doi:10.1130/G23894A.1.
- Thompson, Ida; Jones, Douglas S. (1980). "A possible Onychophoran from the Middle Pennsylvanian Mazon Creek beds of northern Illinois". Journal of Paleontology 54 (3): 588–96.
- Budd, Graham E. 2001. "Tardigrades as 'stem-group arthropods': the evidence from the Cambrian fauna". Zoologischer Anzeiger 240 (3–4): 265–79. doi:10.1078/0044-5231-00034.