Balanoglossus is connecting link between non-chordates & chordates.

Explanation

1. Balanoglossus is an organism which is structurally intermediate between two different groups. - Non - chordates and chordates.
2. Non-chordates do not have notochord whereas, chordates have either notochord or vertebral column in their body.
3. In Balanoglossus, notochord is present in proboscis region and only half notochord is present. Hence, it is called as Hemichordata.
4. Since, it belongs to Phylum Hemichordata, it shows the characters of both the groups chordata and non-chordata.
5. Hence, Balanoglossus is a connecting link between non - chordates and chordates.