Which of the following is a connecting link between invertebrates and non-invertebrates?

Balanoglossus is a connecting link between invertebrates and non-invertebrates. Balanoglossus belongs to phylum Hemichordata which was earlier considered as a sub-phylum under phylum chordata. But, now it is placed as a separate phylum under non-chordata because notochord and postanal tail are absent in it.