Ancient chordates are thought to be most closely related to echinoderms because the embryos of chordates and echinoderms are

Both show similarities in their embryos- Radial cleavage, Indeterminate cleavage and blastopore become the tail end.

Explanation:

Chordates and echinoderms show similarities in their embryological development-

1. Radial cleavage: in there 8 cell stage has 2 different tiers of cells, 4 cells each. Each cell directly above or below another.

2. Indeterminate cleavage: cells can develop into an entire embryo if separated in an early stage.

3. Blastopore turns into the tail end or posterior end except for few molluscs and other protosomes.

age range would be the answer