Hypothesize an evolutionary relationship among the bipinnaria larva of echinoderms, larval and adult tunicates, and lancelets

-Not completely understood, share echinoderm and chordate characteristics

-Chordates/them have pharnygeal slits

-Ambulacraria hypothesis unites echinoderms and hemichordates on the basis of a shared diffuse epidermal nervous system

-Shared tripartite coelom in hemichordates/echinoderms

-Buccal diverticulum now believed to be a synapomorphy of hemichordates only

-Early embryogenesis of hemichordates similar to echinoderms

-Tornaria larva almost identical to bipinnaria larva, suggesting that hemichordates/echinoderms are sister groups

-Sequence analysis of the gene encoding the small subunit of rRNA supports a deuterostome clade