The body of P. marginemaculatus can measure up to 18 millimetres (0.71 in) long, but its front legs can reach 100 millimetres (3.9 in) long. It has eight pairs of legs with six used for walking and the first employed as sensory organs for detecting prey and navigating their environment. Its cephalothorax is wider than it is long and is outfitted with eight eyes. One pair of eyes is located in front and 3 more pairs on the sides. They produce no venom, but instead have arm-like pedipalps and a pair of smaller chelicerae.