Arthropoda: Segmentation the successful formula
Segmentation may have increased the efficiency for burrowing in mud. A line of separate limbs that are repeated down the length of the body seems to have been the most primitive form. Each segment is equipped with its own set of organs - on either side, leg-like projections sometimes accompanied by bristles and feathery appendages through which oxygen could be absorbed, and within the body wall, a pair of tubes opening to the exterior from which waste is secreted. A gut, a large blood vessel and a nerve cord run through all segments from the anterior to the posterior end of the organism and co-ordinates the segmentation. a great variety of these segmented animals have been almost perfectly fossilized in the Burgees shale of the Rocky Mountains in British Columbia, Canada.