The eye of the caecilianRhinatrema bivittatum(Amphibia: Gymnophiona: Rhinatrematidae)

The reduction in the visual system of the Gymnophiona has been noted by many authors. Adult caecilian amphibians eyes are small, covered by skin and sometimes bone, with retinal cells that contain only rod opsins and co-option of structures usually associated with the visual system used for novel sensory structures and functions. Here, we provide a description of the eye of Rhinatrema bivittatum, the first of any rhinatrematid caecilian, and consider its significance for our understanding of the nature of the eye in the last common ancestor of living caecilians. Characters discovered include zonule fibres, an aqueous humour and the remnants of an attachment that could be a protractor lentis muscle.