''Polysacos'' is an extinct genus of

multiplacophora Multiplacophora is a stem-group of chitons with a number of plates arranged in 7 rows along the body. They date to at least the Upper Cambrian, but two lower Cambrian fossils- ''Ocruranus'' and ''Trachyplax'' - may extend the range downwards. F ...

ns (chitons) known from articulated

Carboniferous The Carboniferous ( ) is a geologic period and system of the Paleozoic that spans 60 million years from the end of the Devonian Period million years ago ( Mya), to the beginning of the Permian Period, million years ago. The name ''Carbonifero ...

fossils; its seventeen shell plates are arranged in three rows, with seven iterated units. It demonstrates that multiplacophora are related to modern polyplacophora. It was fringed with a ring of hollow spines resembling those of the Ordovician ''

Echinochiton ''Echinochiton'' is an extinct genus of Ordovician chiton Chitons () are marine molluscs of varying size in the class Polyplacophora (), formerly known as Amphineura. About 940 extant and 430 fossil species are recognized. They are also ...

''.

References

Prehistoric chiton genera {{paleo-mollusc-stub