Onychophorans are "living fossils" in the sense that they have changed little in their body shape for about 500 million years. Probably they were the first animals ever to walk; fossils indicate that they lived in shallow marine environments in the Cambrian, in tropical habitats from many parts of the world. With time, they colonized dry land and those that may have remainedin the sea became extinct.
These animals are found in moist, dark places like rotten logs, leaf litter and soil crevices and normally become active at night, when the danger of dessication is less. Although textbooks tend to present much "general" information about onychophorans, the truth is that we know close to nothing about the great majority of the about 90 described species (a similar number is thought to be unknown to science).
Onychophorans are exceedingly rare and probably endangered in many habitats.
Julian Monge - Najera
State Distance Education University (UNED), Costa Rica