organisms are classified on the basis of fate of blastopore... i.e proterostomes and dueterostoms ... deuterostoms are those in which blastopore ( formed during the embryonic development) develops into anus in other words anus is formed before mouth.. eg. echinodermata to chordates and protostorms are those whose blastopore develops into mouth or in other words mouth is formed before anus eg. platyhelminthes to mollusca