Velvet Worms (also called Onychophora) are segmented, caterpillar-like, terrestrial animals somewhat resembling both arthropods and annelid worms. They are generally regarded either as a class of arthropods or as a separate phylum (in which case they are the only animal phylum to include no marine species). About 110 modern species are known separated into two families, with 10 genera. They live in many tropical and subtropical regions worldwide including Mexico, Central America, South America, Africa, Australia and New Zealand. Modern species are fairly small; at least one species reaches lengths of 20 cm (about 8 inches). The best known modern form is Peripatus which was described by Guilding in 1825.

The 2008 IUCN red list of threatened species has no velvet worms listed as recently extinct. Although the Lion's Hill Velvet Worm (Peripatosis leonina) is missing (possibly extinct). This species was listed as extinct since the 1996 red list, but has removed from the extinctions list in the 2003 red list. The justification of the IUCN is: "there is no conclusive evidence that this species is extinct, and given the nature of onychophorans and the lack of research on this group, there is a chance that this species may still be extant, but Critically Endangered as a result of changes to its narrow habitat".