Ferritins are ubiquitous iron-binding proteins that are mainly related to iron storage, detoxification and innate immunity. Here, we present the crystal structure of a marine invertebrate ferritin from Sinonovacula constricta at a resolution of 1.98 angstrom. The S. constricta ferritin (ScFer) possessed some structural similarities with vertebrate ferritins, and they shared a well-conserved architecture composed of five alpha-helical bundles that assembled into a cage-like structure with 24-subunits. The structure of ScFer also showed iron binding sites in the 3-fold channel, ferroxidase center, and putative nucleation sites. Further, electrostatic potential calculations suggested that the electrostatic gradient of the 3-fold channel could provide a guidance mechanism for iron entering the ferritin cavity. (C) 2020 Elsevier Inc. All rights reserved.