They are also sometimes known as '''sea cradles''' or '''coat-of-mail shells''' or '''suck-rocks''', or more formally as '''loricates''', '''polyplacophorans''', and occasionally as '''polyplacophores'''.
Chitons have a shell composed of nine eight separate shell plates or [[Valve (mollusc)|valves]].<ref name=EB1911/> These plates overlap slightly at the front and back edges, and yet articulate well with one another. Because of this, the shell provides protection at the same time as permitting the chiton to flex upward when needed for locomotion over uneven surfaces, and even allows the animal to curl up into a ball when dislodged from rocks.<ref>{{cite journal |last1=Connors |first1=M.J. |last2=Ehrlich |first2=H. |last3=Hog |first3=M. |last4=Godeffroy |first4=C. |last5=Araya |first5=S. |last6=Kallai |first6=I. |last7=Gazit |first7=D. |last8=Boyce |first8=M. |last9=Ortiz |first9=C. |year=2012 |title=Three-Dimensional Structure of the Shell Plate Assembly of the Chiton Tonicella Marmorea and Its Biomechanical Consequences |journal=Journal of Structural Biology |volume=177 |issue=2 |pages=314–328 |doi=10.1016/j.jsb.2011.12.019 |pmid=22248452}}</ref> The shell plates are encircled by a skirt known as a [[girdle (chiton)|girdle]].