The spatial resolution of the pinhole eyes of giant clams (Tridacna maxima)

Land, Michael F (2003) The spatial resolution of the pinhole eyes of giant clams (Tridacna maxima). Proceedings of The Royal Society B: Biological Sciences, 270 (1511). pp. 185-188. ISSN 1471-2954

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Giant clams (Tridacna spp.) have several hundred small pinhole–type eyes on the exposed mantle. They respond by withdrawing the mantle to movements of dark objects, even if these cast no shadow on the animal as a whole. I investigated this ‘sight reaction’ using black and white square–wave gratings whose phase abruptly changed so that the white areas became dark and vice versa. Gratings with periods of 13.5° were ineffective, but gratings of 20.7° caused partial retraction of mantles or siphons. This implies an acceptance angle for the best–resolving eyes of between 8.7° and 21.8°. A single black spot was effective if its angular diameter was 13.5°but not 11.7°. The mean threshold for the pure dimming of a large field was a decrease of 12.3percnt;, but responses increased in strength up to a dimming of 35%. Anatomically the eyes are ca. 400 μm deep from aperture to receptors, the aperture has a mean diameter of 90 μm and the receptors are 25 μm across. This gives an angular acceptance angle for single receptors of 16.5°, which is completely consistent with the behavioural measurements.

Item Type: Article
Keywords: Giant Clam; Tridacna; Mollusc; Pinhole Eye; Resolution; Vision
Schools and Departments: School of Life Sciences > Biology and Environmental Science
Depositing User: Michael Land
Date Deposited: 06 Feb 2012 19:20
Last Modified: 25 Jul 2012 11:29
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