A large lattice-like axial structure found in some flagellated protists which extends alongside the axoneme. Protein components of the paraflagellar rod are likely implicated, among other, in adenine nucleotide signaling and metabolism, and in calcium signaling. [ http://www.ncbi.nlm.nih.gov/pubmed/26688619 http://www.ncbi.nlm.nih.gov/pubmed/19879876 GOC:cilia http://www.ncbi.nlm.nih.gov/pubmed/26199333 ]