melanosclerite (mel-a-no-scle'-rite). A problematic organic (chitinous) microfossil with a dense wall and a variety of forms ranging in size from approximately 50 μm to several millimeters. It is present in organic residues from the Paleozoic of Laurentia, Baltica, and Laurasia and thought to have an affinity with hydrozoans (Cashman, 1996).