Ray

They are very close. Rays and sharks together make up the cartilaginous fish, sharing a skeleton of cartilage rather than bone, tooth-like skin denticles, no swim bladder, and internal fertilisation with claspers. Rays are essentially the branch of that group that took up life on the sea floor and became flattened for it, with the pectoral fins expanded into a disc and the gills and mouth moved underneath. Some in-between forms, such as the guitarfishes and the angelsharks, blur the line. So a ray is not a separate kind of animal from a shark so much as a specialised, bottom-dwelling design within the same broad family.

Much less than its reputation. A stingray never attacks, and its spine is purely defensive, used only when the animal is trodden on, pinned, or grabbed, when it flips its tail up and drives the barbed, venom-coated spine into the attacker. The wound is very painful, can cause swelling and, if the barb breaks off, infection, and needs medical attention, but it is rarely serious and deaths are extremely rare, the best-known being the naturalist Steve Irwin in 2006, killed by a spine to the chest. In shallow water where stingrays rest buried in the sand, the standard precaution is the stingray shuffle, sliding the feet along the bottom rather than stepping down, so a hidden ray feels you coming and swims off.

The manta is a ray that abandoned the sea floor. Instead of lying flat and crushing shellfish, it swims constantly through open water, flapping its huge triangular wings, and it feeds by filtering plankton, funnelling water into its wide mouth with a pair of flexible head fins and straining out the tiny animals on comb-like plates on the gills. Mantas are enormous, with wingspans up to about 7 metres in the largest species, they have the biggest brain of any fish, and they have passed the mirror test for self-recognition. They also have no functional tail spine, so unlike a stingray a manta cannot sting, and it is harmless to swimmers and divers.

Several factors combine. Many rays live in shallow coastal waters, estuaries, and even rivers, exactly the places most affected by fishing pressure, habitat destruction, pollution, and dams, so they have nowhere to retreat. Their flattened shape means they are readily caught in the trawl nets and gill nets set for other fish, as bycatch that is often not even targeted. Some, especially the sawfishes and guitarfishes, have body parts that are highly valued, and the manta and devil rays are hunted for their gill plates for traditional remedies. And like sharks, most rays grow slowly and produce few young. The overall result is that a higher proportion of ray species than shark species is now listed as threatened.