Question

Why are hemichordates placed as an independent phylum under non-chordata?

Answer 1

Hemichordata:

1. Hemichordates nowadays are placed with non-chordates because they lack a true notochord. Instead a rudimentary structure of a notochord known as stomochord is present.
2. Pharyngeal gill slits, dorsal nerve cord and heart are present.
3. Earlier hemichordates were kept in phylum chordata due to the presence of a buccal diverticulum which was supposed to be a rudimentary notochord however later it was found that this structure does not show any resemblance to the notochord and DNA analysis showed that hemichordates are much closer to echinoderms than chordates.
4. Hence, they were then separated from chordates and made a different phylum.