Chiton

Chiton, the best known of those simple types of the Gastropods known as the Isopleura, which are elongated forms retaining the primitive bilateral symmetry lost in all other Gastropods. In Chiton the nephridia and genital ducts are paired and bilaterally symmetrical, and thus retain a trace of a possibly original segmentation. The ctenidia or gills support this idea, as they are present in sixteen pairs. The shell consists of a series of overlapping plates on the dorsal side of the body: the microscopic structure of these plates is somewhat complex. The radula or the toothed-tongue, with which it obtains its food, is well developed; it thus differs markedly from its allies Chaetoderma and Neomenia. In addition to the ordinary eyes there are many simple eyes on the dorsal surface. Chiton is an old genus, dating from the Carboniferous. It is common round the English coasts, creeping over rocks by its broad flat foot.