how many species of polyplacophora
Polyplacophorans include about 600 extant species. Entirely marine, they inhabit hard bottoms and rocky coasts in all of the world's oceans. Although commonly intertidal, living chitons have been dredged from waters as deep as 7000 m. Of the two subclasses, Paleoloricata and Neoloricata, only the latter is represented by living examples. The shell plate of a neoloricatan extends beneath the adjacent plate. Lacking this feature, the paleoloricatates are considered less derived.