Polyplacophora

Polyplacophora is the order of Mollusca which includes the Chitons in which the body is protected by a shell formed of eight overlapping platesi The group is of great geological antiquity, and includes some of the most primitive of living Mollusca. The body is bilaterally symmetrical, and the organs are all paired and metamerically repeated; this may be a trace of segmentation in the ancestor of the Mollusca.