Polysacos

{{Short description|Extinct genus of molluscs}}

{{Speciesbox

| fossil_range = 335

| genus=Polysacos

| species = vickersianum

| parent_authority = Vendrasco et al., 2004

| authority = Vendrasco et al., 2004

}}

Polysacos is an extinct genus of multiplacophorans (chitons) known from articulated Carboniferous fossils; its seventeen shell plates are arranged in three rows, with seven iterated units. It demonstrates that multiplacophora are related to modern polyplacophora.{{Cite journal | last1 = Vendrasco | first1 = M. J. | last2 = Wood | first2 = T. E. | last3 = Runnegar | first3 = B. N. | title = Articulated Palaeozoic fossil with 17 plates greatly expands disparity of early chitons | journal = Nature | volume = 429 | pages = 288–291 | year = 2004 | pmid = 15152250 | doi = 10.1038/nature02548|bibcode = 2004Natur.429..288V | issue=6989}} It was fringed with a ring of hollow spines resembling those of the Ordovician Echinochiton.