The sister taxon of the chordata is the
mollusca
arthropoda
ambulacraria
rotifera

Ambulacraria

Explanation:

Ambulacraria or Coelomopora is an invertebrate clade that encompasses the Echinodermata and Hemichordata within the deuterostomies. This grouping is considered Chordata's sister taxon because it has a common ancestor.

The phylum Chordata is considered the last within the evolutionary range and comprises all vertebrates and some invertebrates such as amphioxus and tunicates. The main feature of this phylum is the presence of notochord in at least one of its embryonic phases. In vertebrates, the notochord will later make room for the Vertebral Column.

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