9. “All vertebrates are chordates but all chordates are not vertebrates”. Justify the statement.
Phylum chordata includes animals characterised by the presence of notochord. This phylum includes sub-phyla urochordata, cephalochordata and vertebrata. In vertebrates, the notochord is replaced by vertebral column, in urochordates and cephalochordates vertebral column is absent. Thus, all vertebrates are chordates but all chordates are not vertebrates as they can be urochordates and cephalochordates also.