Response of the larvae of the sea urchin <i>Centrostephanus rodgersii</i> under light and polarization conditions

In this paper, we investigated the response of the larvae of the sea urchin Centrostephanus rodgersii to unpolarized halogen light, darkness as well as polarized (linear, circular and elliptical) halogen light presented in side view to observation chambers. The larvae exhibited positive phototaxis when exposed to unpolarized, horizontally polarized, elliptically polarized, and circularly polarized light. However, they did not respond to vertically polarized light. In fact, larval swimming behavior after exposure to vertically polarized light was the same as keeping them in the dark. These findings indicate that not only may the larvae of C. rodgersii have photoreceptors capable of detecting light in the visible spectrum but they may also possess the capacity to differentiate between horizontally and vertically polarized light, which might help them navigate. These findings suggest the possibility of aligned photoreceptors in these larvae. In addition, we found that the larvae respond to circularly polarized light. This result is notable as there are few documented cases of circular polarization sensitivity in animals. As they did not appear to have a preference between the left- and right-handed polarizations, one would need to study their photoreceptor cells to determine the mechanism by which they can detect circular polarization. This could pave the way to the development of new polarization detectors based on biological mechanisms.