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.

[1] It was fringed with a ring of hollow spines resembling those of the Ordovician Echinochiton.

This prehistoric mollusc article is a stub.

You can help Wikipedia by expanding it.