Calcitonin-typical suppression of osteoclastic activity by amphioxus calcitonin superfamily peptides and insights into the evolutionary conservation and diversity of their structures.

•Amphioxus, Branchiostoma floridae, possesses three calcitonin (CT) family peptides designated as B. floridae CT family peptides 1–3 (Bf-CTFP1–3).•Bf-CTFPs suppress the ostoclastic activity of goldfish scales via the CT receptor.•Bf-CTFPs and salmon CT share common essential amino acids for ligand activity.•The alpha-helical structure of Bf-CTFP1 and 2 is conserved with that of teleost CT.•Bf-CTFP3 has a unique alpha-helical structure.