User:Jtwsaddress42/Projects/Project 4/Sections/Chapter 2/The early genetic and morphological instability of Deuterostome evolution

Early on, Bilaterians bifurcated into two major superphyla. Each superphyla is characterized by differences in their modes of development - Protostomes which develop the mouth first, from the blastopore during gastrulation, and then the anus secondarily; and the Deuterostomes which develop the anus first via the blastopore during gastrulation, and then the mouth secondarily. This distinction between protostomes and deuterostomes appears to be, either the consequence of an inversion of the dorsal-ventral (DV) axis of the body in a branching population of early protostome bilaterians; or, the parallel branch of bilaterians that resulted from the breaking of radial symmetry, and establishment of bilateral mirror symmetry, at the origin of the bilaterians as the anterior-posterior axis (AP-axis) and dorsal-ventral axis (DV-axis) was established.

Protostomes can be grouped into two types as well: ecdysozoa and lophotrochozoa. Protostomes as a superphyla are a highly diverse group that comprise the vast majority of animals in terms of phyla and body plans, but deuterostomes are a rather more eclectic group that comprised of three phyla: echinoderms, hemichordates, and chordates. Hemichordates seem to share features of both superphyla, as well as unique features of it's own. Much of what is understood about the deuterostomes comes from studies and observations of chordates, and vertebrates in particular - the other two phyla being less understood.

Within the deuterostomes there appears to have been a great deal of genomic instability, replication, and reorganization within the genetic toolkit that constrains the ontololgy of developmental epigenesis prior, and well into, the early evolutionary establishment of these three phyla and their respective body plans.

While instability might seem to be a highly undesirable situation, for somatic selective systems that succeed in adapting, it can be a wellspring of creativity leading to novel results.