What 4 structures do all vertebrate embryos initially have?

Vertebrates are group into the phylum of chordate.

Although all the chordate physically have a great differences but during the embryonic development there are 4 similar structure:

1. have gills (which depend on which class if for fishes the gills will use for respiration if for mammals gills will develop for hearing)

2. have notochord (which will develop into back bone)

3。nerve chord

4. tail