mollusc polyplacophoran WIKIPEDIA:Polyplacophora Chitons are small to large marine molluscs in the class *Polyplacophora*, which formerly was known as *Amphineura*. There are approximately 940 extant and 430 fossil species recognized. These molluscs are also sometimes commonly known as sea cradles or "coat-of-mail shells". They are also sometimes referred to more formally as loricates, polyplacophorans, and rarely as polyplacophores. Chitons have a dorsal shell which is composed of eight separate shell plates or valves. These plates overlap somewhat at the front and back edges, and yet the plates articulate well with one another. amphineura chiton chíton loricate polplacophore polyplacophora requires discussion