Data from: The sea urchin Diadema africanum uses low resolution vision to find shelter and deter enemies

Many sea urchins can detect light on their body surface and some species
are reported to possess image-resolving vision. Here we measure the
spatial resolution of vision in the long-spined sea urchin Diadema
africanum, using two different visual responses: a taxis towards dark
objects and an alarm response of spine-pointing towards looming stimuli.
For the taxis response we used isoluminant visual stimuli to discriminate
spatial vision from phototaxis. Individual animals were placed in the
centre of a cylindrical arena under bright down-welling light, with
stimuli of varying angular dimensions placed on the arena wall at
pseudorandom directions from the centre. We tracked the direction of
movement of individual animals in relation to the stimuli to determine
whether the animals oriented towards the stimulus. We found that D.
africanum responds by taxis towards isoluminant stimuli with a spatial
resolution of 38° - 89°, assuming a contrast threshold of 10%. The visual
acuity of the alarm response of D. africanum was tested by exposing
animals to different sized dark looming and appearing stimuli on a
monitor. We found that D. africanum displays a spine-pointing response to
appearing black circles with a spatial resolution of 60° - 116°, assuming
the same contrast threshold as above.