Velvet Worms: Onychophora

Velvet worms have bilateral symmetry (bye-LAT-er-uhl SIH-muh-tree) and can only be divided into similar halves along one plane. They resemble caterpillars and have long, soft, and flexible bodies. Adults measure from 0.5 to 8 inches (13 to 203 millimeters) long. Most range in color from black to blue, red, brown, or gray. Some species are striped or have beautiful patterns. Their skin, or exoskeleton, is very elastic and covered with small bumps called papillae (pah-PIH-lee). The papillae are made up of small scales that give them a velvety appearance. Larger papillae have a single sensory bristle that helps velvet worms to feel their surroundings.

Along the sides of the bodies are breathing holes, or spiracles (SPIH-reh-kulz). The spiracles lead to a network of respiratory tubes inside the body, similar to insects and spiders. The head has a pair of soft antennae, clawlike jaws, and soft, fleshy papillae on either side of the mouth. Inside the mouth is a rough, tonguelike structure that helps to grind food. The cone-shaped legs are stumpy and unsegmented, but there are 13 to 43 pairs of legs, depending on the age, sex, and species of velvet worm. Each leg is tipped with 3 to 5 pads and a pair of claws.