ABSTRACT

On the Gulf Coast, as in other areas, ostracodes have been much used in interpreting paleoenvironments. Such use may be enhanced by study of the ocular structures including eyespots. Eyespot morphology appears to relate to light levels, which in turn are related to water depths; thus, a new means of reconstructing water depths may be available.

Eyespots from two species of Echinocythereis from modern sediments along the Gulf Coast were studied using polished sections, and electron and light microscopy. The inner surface of an eyespot is undulating with a central convex portion and posterior concavities, each having a small radius of curvature compared to the convex outer surface. Light is converged most strongly by the central area and focused in the underlying eye space. Astigmatism occurs as light passes through the areas away from the center; in these cases the focus is beyond the eye cavity in the absence of a tapetal layer. Comparison of a modern and an extinct Eocene species of Echinocythereis indicates similar morphology and presumably similar functioning. There is a potential for discerning modern morphology as related to water depth and applying such knowledge to fossil forms and their environments.