Archerd Shell Collection> Shell Classes > Polyplacophora > Chiton Eyes
What Do They See?
Not all chitons have eyes, and most depend on tactile or chemically sensitive nerve endings to find food. However, tropical water chitons in the subfamily Toniciinae do have fully formed eyes. At the left, Lankester (1906) shows a remarkably developed shell eye, based on microscopy done in the 19th century.
The pigmented, primary eye (ocellus) numbers in the thousands. It projects from the mantle upwards through minute holes in the anterior plates of the chiton. These eyes are arranged in diagonal rows. The tiny secondary eye spots ("aesthetes") are not pigmented and have no retinal cells. Several thousand may be found in a 2 millimeter patch of the integument. Their function is now believed to be both chemosensory and secretory (Beesley et al., 1998).
Lankester stated that this chiton can detect disturbances in the water, as affected by light. This suggests some degree of centralized processing of the visual information.
Archerd Shell Collection> Shell Classes > Chitons > Chiton Eyes