The protochordate Ciona intestinalis has a protein like full-length vertebrate fibrinogen.

In a recent review, a putative fibrinogen-like protein in the protochordate Ciona intestinalis was noted. Unfortunately, computer-directed splicing had omitted several exons, mistakenly generating a single long polypeptide chain. In fact, 3 consecutive genes exist, the translated versions of which are homologous to individual vertebrate fibrinogen chains. The circulating form is likely a 6-chain covalent dimer, just as occurs in vertebrates.