Question

Is notochord is absent in adult petromyzon

Answer 1

The members of sub-phylum - Vertebrata possess notochord during the embryonic stage. But in adults thenotochord is replaced by a cartilaginous or bony vertebral column. ... Thus, the absence of notochord inadult vertebrates suggest that all vertebrates are chordates but all chordates are not vertebrates.

Answer 2

$\sf yes \: \: \: \: notochord \: \: \: \: is \: \: absent \: \: \: in \: \: \:$

$\sf adult \: \: \: \: petromyzon$