The onychophoran ventral nervous system consists of two
eyes—one at the base of each antenna, a brain, and longitudinal
ventral cords having transverse connections but lacking the
ganglia (bundles of nerve cell bodies) found in arthropods and
annelids. Onychophoran eyes have a chitinous lens and retina
and are used to direct viscous adhesive at prey and predators.
Velvet worms avoid light between 470 and 600 nm; this photonegative
behavior may protect them from desiccation. Caveadapted
Speleoperipatus and Peripatopsis alba are eyeless and
lack body pigment. Sensory bristles on body papillae and sensory
antennae orient the velvet worm to touch and perhaps to
water vapor.