~ Rays ~
Rays are a type of flattened fish and all rays are closely related to sharks. Rays evolved from sharks and belong to the same group as sharks, called Elasmobranchii. These social animals live in seas all over the world. Some rays often congregate in large groups of up to thousands of individuals, but other rays live alone.
Unlike other fish, rays have no bones, instead their skeleton is made of cartilage. Cartilage is a tough, fibrous substance, not nearly as hard as bone. Sharks also have skeletons made of cartilage.
The earliest known rays date from about 150 million years ago during the Jurassic period. Since rays have only cartilage, fossil rays are rare, but like sharks, their teeth, composed of very hard enamel, fossilize well. Many fossilized teeth and some fossilized spines have been found.
Many species of rays have spines on their tails. The spines can poison other animals when stung. Some rays have long tails while other species have short tails. Some rays have a series of thorns on their body as further defense against predators. The ray's tail varies from species to species. It ranges from stubby, on species like the shorttailed electric rays, to incredibly long on the rays like the sting rays.
Rays defend themselves from predators in many different ways. Some use their whip-like tail to lacerate, some sting with a poisonous stinging tail, electrical rays give electrical shocks up to 200 volts, and some have hard, bony spines that puncture their victims. Teeth are not used very much by rays as a defense, but some can bite. A ray can burrow itself into the sea bed and be completely camouflaged by the sand; which is probably their best defense. Rays don't normally attack humans. Some have a sting that is deadly. Most stings to humans happen when they are stepped on or when a ray is being removed from a fishing line or net.
There is a huge range of color variation among rays. Colors can even vary from male to female in the same species of some rays. The size of rays can vary as much as their color, from just a few inches to over 25 feet wide. The short-nose electric ray is the smallest of rays and is about the size of a small plate (approximately 4 inches across and weighs about 1 pound). The manta ray is the largest of rays and can measure over 25 feet wide and can weigh thousands of pounds. Most rays measure and weigh between these two extremes. More than half of all ray species are over 20 inches long. Rays are some of the largest fish in the oceans.
All rays have a flattened body and an elongated tail. The pectoral fins are large and connected to the body to form the ray's disc-like form. The shape of the ray's body differs from species to species and may be circular, oval, wedge-shaped or triangular. Some body shapes are adapted for living on the sea bed and others are adapted for almost constant swimming.
There are about 500 different species of rays and skates, which are divided into 18 families. These different families of rays are very different in the way they look, live, and hunt. They have different shapes, sizes, color, fins, teeth, habitat, diet, personality, method of reproduction, and other attributes.
Rays are carnivores. Just a few examples of their diet would be fish, crustaceans, and mollusks. Rays mostly hunt on or near the bottom of the ocean. The manta ray, however, is a filter feeder, sieving small prey as they swim almost continuously. Other rays are active hunters searching for bottom-dwelling animals like mollusks and crustaceans. The electric ray stuns its prey with electricity.
Rays have a high ratio of brain weight to body weight; they are probably very intelligent, even smarter than sharks. They are known to be very curious animals, often approaching a diver and simply observing the intruder.
Rays live in oceans and seas all over the world. Rays live mostly on or near the sea bed. Different ray species are found in habitats ranging from close to shore to extreme depths of over 10,000 feet deep.
Rays swim very differently than other fish. They are propelled through the water with their powerful, pectoral fins which ripple and flap, much like a bird's wings. Their large pectoral fins also let them glide through the water. Some rays can even jump above the water. Other ray species are coated with a slimy mucous which reduces the surface tension and drag of the water and increases their swimming speed. Rays lack a swim bladder and use their oily liver to maintain buoyancy just like sharks do. When a ray stops swimming, it sinks down to the sea bed.
Some rays are oviparous (laying eggs) while others reproduce via ovoviviparity (this is when animals hatch from eggs, but the eggs hatch and the babies develop inside the female's body; there is no placenta to nourish the pups). All skates are oviparous. Fertilization is always internal. Both rays and skates have a long gestation period and produce relatively few young. The growth of ray populations is slow. Reproduction and growth rates of ray populations are the same as for sharks.