The phylum Onychophora includes around 110 described species (and likely a similar number undescribed) of caterpillar-like relatives of arthropods. The first description of a living onychophoran was in 1826 (misinterpreted as a leg-bearing "slug", a mollusc). All living species are terrestrial, but a number of marine species are known from the fossil record going back to the Early Cambrian over 500 million years ago. Living Onychophora are found in humid habitats, stashing themselves away in burrows or other retreats and becoming inactive during dry periods. During wet periods, they can be found sifting through leaf litter. (Brusca and Brusca 2003) With the exception of just a few species, onychophorans have not been well studied and the New World fauna is especially poorly known (Read 1988).