Stingrays are probably the most recognized type of ray. They are most easily identified by their elongated, thin tails with barbed stings. Most stingrays' tails have venom glands, which inject an incredibly painful toxin when the sting is used. Thankfully, stingrays only sting out of self defense. A diver is unlikely to be stung by a stingray unless he causes the creature to feel threatened.
Stingrays may also be identified by their characteristic diamond shape, and by the fact that they are frequently found half-buried in the sand rooting for food. Many rays spend the majority of their time on the sea floor; however some stingrays, such as spotted eagle rays, are more commonly observed free-swimming.
Stingrays are oviviparous, meaning that their eggs develop and hatch inside the mother, who then gives birth to live young. These rays can be found in all parts of the world, even in fresh water. Commonly recognized species of stingrays include the southern stingray, the spotted eagle ray, and the blue spotted ray.
Although they do not have stingers, manta rays are technically a type of stingray; they have simply lost their stings through the process of evolution. Manta rays can be easily identified by their great size. The largest manta rays have a wing spans up to 25 feet and weigh as much as 3,000 pounds!
Despite their great size, manta rays are not vicious predators. They usually filter feed and have large padded lobes on either side of their heads to direct food into their mouths.
Manta rays are incredibly graceful underwater, and can move quite quickly with seemingly effortless movements of their pectoral fins. Manta rays even breech occasionally, leaping from the water and backflipping in the air.
Skates appear quite similar to stingrays, but there are a few differences between skates and rays that divers can use to identify a skate underwater. Skates do not have stings. Instead, they have sharp barbs along their spines or on their tails for defense. Skates also have wider tails than stingrays, with small fins near the tip of the tail. Finally, skates are round or triangular shaped with elongated noses, as opposed to the typical diamond shape of most stingrays.
Skates have a different reproductive cycle than stingrays. Stingrays are oviviparous, while skates are oviparous, meaning that they lay eggs which hatch outside of the female's body. Skates are only found in marine habitats.
Electric rays have a different form of defense from other rays. Stingrays sting, skates defend themselves with barbs, and manta rays are too large to have any natural predators. Electric rays are smaller than many other types of rays, and do not have barbs or stings. Instead, they stun their prey with electric shocks.
While all rays have a highly-developed electric sense, electric rays have special electric organs on either side of their heads. These organs can generate between 50-200 volts and 30 amperes of electricity, enough to shock or injure a human, and definitely enough to take out small prey. Electric rays have such an acute electric sense that they are thought to be the most electrically sensitive of all animals.
Electric rays are usually 1 to 6 feet in diameter, and have a more rounded shape than other rays. They have rounded dorsal fins and thick tails. Unlike other rays, electric rays use their tails to swim, not their pectoral fins. Electric rays are found at many depths, from shallow waters to as far as to 3000 feet below the surface.