The ray most often seen by British divers is the thornback (pictured), named after its numerous large spines. Its close relative, the magnificent common skate (wingspan up to 2m, twice that of the thornback), was once abundant but has been fished to virtual extinction in UK waters. Now thornback populations seem to be declining, too (visit www.sharktrust.org)

Many rays possess small organic batteries that produce a weak electric field for navigation in dark or murky water. Electric rays have huge batteries that can create discharges of up to 220V for defence and stunning prey. They have a more rounded body than most rays and are rarely seen in our waters, but if you meet one, stay back!

Rays are similar to sharks in many ways and can be thought of as flatened versions of their cousins. Much of their width, however, is produced by hugely enlarged pectoral fins. These flap in an undulating way to give propulsion and create a wonderful impression of flying.

Rays feed on bottom-living creatures such as flatfish, molluscs, crabs and shrimps. They pounce on a victim, and can smother it with their wings before seizing it in their mouths. Their teeth are well suited to crushing and grinding the sort of prey that comes wrapped in a carapace or shell.

Rays are well-adapted to spending much time resting on, or partially submerged in, a sandy or muddy seabed. If they were like most fish and drew in water for breathing through the mouth, which is on the underside of the body, their gills would get clogged with sediment. Instead, they draw in water through openings called spiracles on top of their heads.

The classic mermaids purse, a dark rectangular case with an elongated horn at its corners, is a rays egg-case. A female thornback will lay about 20, each giving rise to a perfect miniature ray after about five months. Rays take several years to reach breeding age which, along with their relatively small number of young, makes them vulnerable to over-exploitation.