The spiny wrigum replaced its ancestor the snow trunksucking worm. It has grown more body segments to better move and bigger breathing holes in the sides of its body. It has developed a 4th jaw to help it eat an dig better. Like its ancestor, the tips of its mandibles have a chemical that helps melt the snow and frozen ground as it digs through them. It has also evolved spines on its back which help protect it when it comes to the surface. They can fold the spines flat on their body when they are digging through the soil.