Note
Three structures in the dermis of the dorsal arm plate (DAP) of the brittlestar, Ophiocoma wendti, appear to comprise a photoreceptor system. The upper surface of the DAP bears transparent, knob-like, microscopic structures which are expanded peripheral trabeculae (EPT) of the calcite stereom. The EPT are part of the photoreceptor system and can facilitate light transmission through the DAP by decreasing light refraction, reflection and absorption that occur at stereom/stroma interfaces. Bundles of nerve fibres located below the EPT are a second component of the system, and may function as primary photoreceptors.