Fine arrangement of photoreceptors in retina and mode of vision in beaked sea snake,Enhydrina schistosa(Daudin, 1803) (Reptilia: Hydrophiidae)

Abstract

The role of eyes was discussed in the beaked sea snake (Enhydrina schistosa) living in the open sea. Fine scanning electron microscope (SEM) images of the cellular arrangement were taken based on histological preparations of the retina. The retina possesses the usual layers of the vertebrate eye and is composed of only cone photosensitive cells lacking rods. Ophidian double cones were not found in the cell composition. Measurements of cone densities and dimensions showed their density in the ventral quadrant was more than that in the dorsal, temporal and nasal quadrants. The ventral specialized retina could be corresponding to surveillance of aerial predators. The presence of three-layered spectacle, single-type, large and dispersed photosensitive cells was evidence of the low visual capability of the eyes in E. schistosa.