More than black and white

Evolution has discovered interesting shapes and colours to fill the potential niches of the earth, and rays are one of the most creative examples. Taeniura lymma, the blue spotted fantail ray, is a member of the Dasyatidae family of stingrays. Although it harbours a potential sting for the unwary, this shy ray will only use it in defence. It lives in the shallow waters of tropical reefs throughout much of the world, including the western Pacific, and represents a taxon that has much to teach us about evolution and especially about vision.

Rays have a truly aquatic, piscine eye (BJO cover, October 2004), although there are differences in ocular morphology since the elasmobranchs (sharks, skates, and rays) diverged from the bony fish (teleosts) long ago. In contrast to teleosts, which have fixed pupils, rays, and most other elasmobranchs, with the exception of deep sea species, have highly mobile pupils. T lymma displays a conventional round pupil in scotopic conditions but a rather oddly shaped pupil under phototopic conditions, as can be seen on this month’s cover. There is a flap, known as the operculum pupillare, …