Which Phylum is Most Closely Related Developmentally to the First

Question

Which phylum is most closely related developmentally to the first vertebrates?  
A) Echinodermata
B) Arthropoda
C) Mollusca
D) Annelida
E) Chelicerata

Accepted Answer

Echinoderms are the most closely related phylum developmentally to the first vertebrates. They both share bilateral symmetry during embryonic development and possess similar regulatory genes for the formation of the nervous system, which suggests a common ancestor. Additionally, echinoderms and the earliest vertebrates both have a notochord as a developmental feature.