Protostomes develop a mouth first and then an anus. This is the difference between protostomes and deuterostomes.
In protostome development, there is a spiral radical and indeterminate cleavage. The blastopore becomes the mouth and the coelom forms from the mesoderm.
In deuterostomes development, radial and indeterminate cleavage takes place. The blastopore is the new anus and the coelom forms from budding off the wall of the archenteron.
