Shade-seeking behaviour under polarized light by the brittlestar Ophioderma brevispinum (Echinodermata : Ophiuroidea)

The effect of polarized light on the shade-seeking behaviour of the ophiuro id Ophioderma brevispinum was investigated at the Keys Marine Laboratory, L ong Key, Florida, USA. Animals were collected and placed in a partially sha ded arena. When the ar ena was illuminated with unpolarized light, the numb er of animals settling under the shaded portion of the arena was not signif icantly different from random (N=30, P>0.3). When the arena was illuminated with linearly polarized light, the number of animals settling in the shade d portion of the arena was approximately double what would be expected in a random distribution (N=30, P<0.001). The results are further evidence that O. brevispinum is sensitive to polarized light and are consistent with the hypothesis that polarized light may be used by the animals as an indicator of harmful levels of solar ultraviolet radiation.