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 signalling and metabolism, and in calcium signalling. [ http://www.ncbi.nlm.nih.gov/pubmed/26688619 http://www.ncbi.nlm.nih.gov/pubmed/19879876 http://www.ncbi.nlm.nih.gov/pubmed/26199333 ]