Why are hemichordate not considered as proper chordate?

Answer 1

Hemichordates are not considered true chordates because they lack several key characteristics that define the phylum Chordata. While they possess a structure called a stomochord, which is somewhat analogous to the notochord in chordates, they do not have a true notochord. Additionally, hemichordates lack other critical features such as a dorsal nerve cord and pharyngeal slits that are characteristic of chordates. Thus, despite some similarities, hemichordates are classified in a separate phylum due to these fundamental differences.