Directly observed images through the shell-lenses of Onithochiton neglectus (Mollusca: Polyplacophora: Chitonidae)
In: Molluscan Research. Malacological Society of Australasia: Sydney. ISSN 1323-5818; e-ISSN 1448-6067, more
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| Keywords |
Onithochiton neglectus Rochebrune, 1881 [WoRMS]
Marine/Coastal |
| Author keywords |
Aragonite; invertebrate; low-resolution vision; ocelli; vision |
| Authors | | Top |
- Smith, A.M.
- Peebles, B.A.
- Spencer, H.G.
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| Abstract |
The dorsal shell surface of the New Zealand-endemic chitonid Onithochiton neglectus exhibits ocelli (eyes) associated with sensory organs (aesthetes) penetrating the shell. Each ocellus includes a mineral lens which focusses light onto a retina, potentially able to resolve images. In order to discover the spatial resolution of lenses of O. neglectus, we isolated them, examined their mineralogy with X-ray diffractometry, imaged the constituent crystals with scanning electron microscopy, and mounted them onto a camera to directly observe and record images. Lenses of O. neglectus are aragonitic and therefore birefringent, providing two different focal lengths, possibly one for in-air and one for underwater vision. Chitons may be able to image nearby shapes with visual acuity equivalent to 6/24 (m), a VAdec of 0.25. Onithochiton neglectus lenses can focus images in air about as well as a person with low visual acuity, sufficient to discern shapes and shadows in the surrounding environment. Lenses from subtidal O. neglectus were less eroded than those from intertidal environments; chitons in different habitats exhibit different visual acuity. It is unclear why a few lineages of chitons have developed such complex eyes; we speculate that body-orientation and navigation could be among the advantages driving such development. |
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