First: Some of these creatures could have elastic legs that shoot out in a manner similar to a frog's tongue. The sticky feet would catch on things and then unstick when needed.
Second: This group should have an embryological anomaly I will for lack of a better term call a hox tail. New sets of legs develop from the posterior end of the body as the organism grows. Some species keep growing throughout their lives. Others stop after reaching adulthood. Some have highly specialized legs and must stop after a certain number so as not to become unbalanced. Having a structure such as this allows a large variation in the number of legs for this group. In evolution (assuming these creatures evolved - I haven't decided yet), legs lost in an ancestor do not prohibit descendants from reattaining them. The posterior end "hox tail" can grow an indefinite number of legs as needed.