Phylum vertebrata: New concepts based ... Much of how organisms are classified depends on their shared characteristics. ... Ambulacraria, above Echinodermata and Hemichordata.

Its extreme characteristics suggest that this common ancestor -- one the creature shares with its sister phyla, echinoderms and hemichordates, as well as chordates -- did not have a brain or ...

COCKBAIN1 has suggested an extension of the suture-line theory2 of the origin and significance of pentamerism in the phylum Echinodermata, which depends primarily on the fact that all modern ...