Developmental analysis of the cone photoreceptor-less little skate retina.

The retinal development of elasmobranchs--the superclass comprising sharks, skates and rays--is a poorly understood phenomenon. The clade is diverse in retinal phenotypes, with many sharks and rays possessing rods and multiple cone types. In contrast, the little skate () has only a single type of rod photoreceptor, which is reported to have taken on some physiological and anatomical properties of cones.