C-type natriuretic peptide (CNP) is a third member of the natriuretic peptide family to be identified subsequent to the identification of atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP). CNP has a considerable sequence homology to the ANP and BNP within the 17-residue ring structure formed by a disulphide bond, although it terminates at the second cysteine residue and lacks a C-terminal extension from the ring structure. This C-type natriuretic peptide CNP-38 was originally found in leopard shark (Triakis scyllaum / Triakis scylla).
Suzuki R, Takahashi A, Takei Y. Different molecular forms of C-type natriuretic peptide isolated from the brain and heart of an elasmobranch, Triakis scyllia. J Endocrinol. 1992 Nov;135(2):317-23. doi: 10.1677/joe.0.1350317. PMID: 1474339.