Valve structure and growth in the chiton Lepidochitona cinereus (Polyplacophora: Ischnochitonidae)

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Abstract
Valve structure was investigated using light and scanning electron microscopy and each valve was found to comprise four layers; periostracum (dorsal), tegmentum, articulamentum and hypostracum (ventral). The penetration of the valves by the aesthetes within channels is described and three distinct types of aesthete channels are identified, namely, multiple branch aesthete channels, slit ray aesthete channels and jugal sinus aesthete channels. The distribution of the different aesthete channels within the various valves is defined and their relationship with the valve external sculpturing is described. The process of valve growth by marginal increment is discussed in relation to the formation of the aesthetes.