Grypania is an early, tube-shaped fossil from the Proterozoic eon. The organism could have been a giant bacterium or bacterial colony, but because of its size (over one centimeter) and consistent form, is more likely to have been a eukaryoticalga. The oldest probable Grypania fossils date to about 2.1 billion years ago, and the youngest extended into the Mesoproterozoic era. Grypania reproduced asexually.
^M. R. Walter, John H. Oehler & Dorothy Z. Oehler (1976). "Megascopic algae 1,300 million years old from the Belt supergroup, Montana: a reinterpretation of Walcott's Helminthoidichnites". Journal of Paleontology50 (5): 872–881. JSTOR1303584.