Onychophora

Onychophora , small phylum with about 70 species of animals that are often called "missing links" between annelids (phylum Annelida ) and arthropods (phylum Arthropoda ). The thin cuticle and wormlike form of onychophorans are reminiscent of annelids, while the tracheal system and details of embryonic development foreshadow similar developments in arthropods. The unsegmented, stumpy legs with arthropodlike claws are unique. Onychophorans live inconspicuously in surface litter and under fallen logs, where humidity is high and protection against drying is greatest. Ancient onychophorans were marine. Modern species live in widely scattered wet, warm to temperate habitats in South Africa, Central America, and New Zealand, suggesting a much wider distribution of terrestrial forms in the past. The 10 genera are often referred to collectively as Peripatus.

Onychophora (velvet worms, Peripatus) A phylum comprising animals that combine annelid and arthropod features and that may be an evolutionary link between the two. They first appeared in the Cambrian (see AYSHEAIA PEDUNCULATA), since when they have changed little. The body is approximately cylindrical and slug-like, but covered with bands of tubercles covered by scales, and with 14 to 43 pairs of legs. The anterior bears antennae. The mouth is in a ventral position, flanked on either side by claw-like mandibles and oral papillae. Reproduction is oviparous, ovoviviparous, or viviparous. Many onychophorans are brightly coloured blue, green, or orange; others are black. There are about 70 species, found only in humid, tropical habitats.