This accompanied or facilitated other important evolutionary developments: the bilaterian body plan, the coelom, and metamerism, in which the body was built of repeated "modules" which could later specialize, such as the heads of most arthropods, which are composed of fused, specialized segments.
This facilitated or accompanied other significant evolutionary advancements: the bilateral body plan, the coelom, and metamerism, which involved repeating "modules" that could later specialize, such as the segmented heads of most arthropods.