Onychophora (from Greek, onyches, "claws"; and pherein, "to carry"), commonly known as velvet worms, is a phylum of elongated, soft-bodied, many-legged bilaterans. They prey upon smaller animals such as insects, which they catch by squirting an adhesive slime. Approximately 200 species have been described, although many more likely exist. The two extant families of velvet worms are Peripatidae and Peripatopsidae. They show an unusual distribution, with the peripatids being equatorial and tropical, while the peripatopsids are all found in the southern hemisphere. It is the only phylum within animalia that is wholly endemic to terrestrial environments. Velvet worms are considered close relatives of the Arthropoda and Tardigrada. This makes them of palaeontological interest, as they can help reconstruct the ancestral arthropod. In modern zoology, they are particularly renowned for their curious mating behaviour and for bearing live young.
Members of the two families differ in their number of legs (generally greater in peripatids), the position of their gonopore (on a more posterior body segment in peripatopsids), and their reproductive habits.