“All vertebrates are chordates but all chordates are not vertebrates”. Justify the statement.

Explanation

All the vertebrates are chordates because all of them have three basic features:
(i) All the chordates possess a notochord
(ii) All the chordates have a dorsal, hollow nerve cord
(iii) All chordates have pharyngeal gill slits in their life cycle.
All the chordates are not vertebrates because vertebrates have vertebral column. It is not present in prochordate and agnatha. They have only notochord that is not replaced by vertebral column.