Why are hemichordates considered an intermediate group between non-chordates and chordates?
Hemichordates possess a stomochord in the collar region, which is similar in function to the notochord but structurally different. This places them between non-chordates and chordates.
Ref: NCERT Class 11 Biology Chapter 4: Animal Kingdom Basis of Classification - Symmetry Coelom Segmentation