- do not have a true body cavity. Also, an excretory system is absent, yet all genes related to the excretory system are present except for Osr, which is essential for the development of such a system. In acoelomorphs, which have gone through rapid evolutionary rates and chromosomal rearrangements, about 60% of the genes shared between protostomes and deuterostomes are missing. How many of these genes, which are present or absent in Xenoturbella, will require whole-genome sequencing.

While other animals that are diploblastic