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First published online November 5, 2004
Journal of Experimental Biology 207, 4249-4253 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.01286

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Spatial vision in the echinoid genus Echinometra

Erin Blevins and Sönke Johnsen^*

Biology Department, Box 90338, Duke University, Durham, NC 27708, USA

View larger version (26K): [in a new window]   Fig. 1. (A) The experimental arena used in the study. The elliptical hole in the side of the tank serves only to show the inside and is not found on the actual tank. (B) Downwelling irradiance at the floor of the arena (in 1013 photons cm-2 s-1 nm-1) as a function of wavelength (in nm).

View larger version (21K): [in a new window]   Fig. 2. The mean bearings of the echinoids. (A-C) Un-normalized bearings. (D-F) Bearings relative to the targets (represented in scale above each graph). Each red line shows the length and direction of the mean bearing for the four trials with one echinoid. The black lines show the means of these mean bearings. 95% confidence ellipses are shown in blue. Circles represent E. lucunter; triangles represent E. viridis.

View larger version (14K): [in a new window]   Fig. 3. The minimum contrast threshold required to detect the presence of a 33° black target for a given spatial resolution. The graph is calculated by convolving the image of the target with the modulation transfer function for a given spatial resolution and then determining the maximum contrast of the convolved image (see Johnsen et al., in press for details). The images above the graph show the appearance of the target when viewed by visual systems with spatial resolutions of 1°, 33°, 60° and 120° (left to right).

View larger version (71K): [in a new window]   Fig. 4. (A) Test of E. lucunter with two spines. Off-angle light (gray arrows) is absorbed and reflected by the spines. Light within the acceptance angle, (white arrow), reaches the body wall between the spines and is detected. (B) E. lucunter in a typical shelter. (C) View of B at a spatial resolution of 33°. Scale bars are 20°, which implies that the center of the viewing echinoid is approximately 6 cm from the center of the pictured echinoid.