General About Onychophora

Onychophorans are carnivorous animals, which inhabit tropical and temperate forests of the southern hemisphere and at the equator. One of the most striking peculiarities of velvet worms is their "shooting" behaviour with a glue-like slime, which is used for defence or prey capture (see images below). The slime is extruded via a pair of modified limbs or slime papillae situated on each side of the head. Onychophorans may have between 13 and 43 pairs of walking legs, the number of which varies inter- or intra-specifically. Each leg has a pair of claws, hence the name Onychophora or "claw-bearers" (Greek: onyx = nail/claw and phoros = carry/bear).

So far, about 200 species of velvet worms have been described from two major onychophoran subgroups: the Peripatidae, and the Peripatopsidae. Representatives of these two subgroups might have diverged prior to the break-up of Gondwana 175-140 million years ago. Although onychophorans are closely related to arthropods (e.g., spiders, centipedes, crustaceans, and insects), their external anatomy has changed little since the Early Cambrian. This is why they are sometimes regarded as "living fossils". Because of their conservative anatomy, onychophorans play a key role in understanding the evolution of arthropods.