Rays
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Rajiformes- common rays and skates |
Rays are a 400 species group (superorder Rajomorphii or Batoidea) of cartilaginous fishes divided into seven families. The largest are the manta rays, also known as devil rays and devilfish, due to the horns on their head. Rays are extremely flat but closely related to the sharks. According to recent DNA analyses the catshark is more closely related to the rays than to other sharks. Young rays look very much like young sharks.
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Anatomy
Rays are flat-bodied, and, like sharks, are a species of cartilaginous marine fish, meaning they have a boneless skeleton made of a tough, elastic substance. Rays also are like sharks in having slot-like body openings called gill slits that lead from the gills. Ray's gill slits lie under the pectoral fins on the underside, and a shark's are on the sides of the head. Most rays have a flat, disk-like body, with the exception of the guitarfishes and sawfishes, while most sharks have a streamlined body. Many species of ray have developed their pectoral fins into broad flat wing-like appendages.
The eyes and spiracles are located on top of the head.
Reproduction
Ray eggs, unlike those of most other fishes, are fertilized inside the female's body. The eggs of all rays but female skates hatch inside the female and are born alive. Female skates lay internally fertilized flat, rectangular, leathery-shelled, eggs, with tendrils at the corners for anchorage. Hatched eggs of this type can be found on beaches and are known as mermaids? purses.
Habitat
Most species live on the sea floor, in a variety of geographical regions - many in costal waters, few live in deep waters, most rays have a somewhat cosmopolitan distribution, in tropical and subtropical marine environments, temperate or cold-water species. Only a few species, like manta rays in the upper waters of open sea, live in the open sea or in freshwater. Some rays can live in brackish bays and estuaries. Bottom-dwelling rays breathe by taking water in through the spiracles, rather than through the mouth as most fishes do, and passing it outward through the gills.
Feeding
Most rays have developed heavy, rounded teeth for crushing the shells of bottom-dwelling species such as snails, clams, oysters, crustaceans, and some fish, depending on the species. Manta rays feed on plankton. No ray can kill humans, but the stingray can inflict a painful sting.
Main Types of Rays
Stingrays
Main article: Stingrays
Stingrays, or whiprays (family Dasyatidae), are named for the wounds they inflict by lashing its tail, which are generally much longer than their bodies, that has rows of spines along it; the spines contain a poison that causes pain and/or (depending on the species). Some species' toxins can be fatal to humans.
Eagle Rays
Main article: Eagle rays
Most eagle rays (family Mylobatidae) have one poison-carrying spine on its tail.
Cow Nose Rays
Main article: Cow nose rays
Manta Rays
Main article: Manta rays
Manta rays (family Mobulidae) swim in the upper waters of the open sea, and may weigh up to 3,000 lb. (1360 kg), with a width of up to 22 ft (7 m). Mantas are filter-feeders, unlike most rays. They use their pair of horns at the front of the head to drive small prey into its mouth. The prey is caught in a strainer and swallowed, the ray lets the extra water pass outward through its gills.
Electric rays
Main article: Electric rays
Electric rays, or torpedoes (family Torpedinidae), have organs in their wings that generate electric current. They are used to immobilize prey and for defense. The current is strong enough to stun humans, and it is said that the ancient Greeks used these fish for shock therapy.
Sawfishes
Main article: sawfishes
Sawfishes (family Pristidae) are sharklike in form, having tails used for swimming and smaller pectoral fins that most rays. The pectoral fins are attached above the gills as in all rays, giving the fishes a broad-headed appearance. They have long, flat snouts with a row of tooth-like projections on either side. The snouts are up to 6 ft (1.8 m) long, and 1 ft (30 cm) wide, and are used for slashing and impaling small fishes and to probe in the mud for imbedded animals. sawfishes can enter freshwater rivers and lakes. Some species reach a total length of 20 ft (6 m). Sawfishes are rays, and should not be confused with saw sharks, which are sharks.
Guitarfishes
Main article: Guitarfishes
The guitarfishes (family Rhinobatidae) are have a body structure similar that of the sawfish.