Rays (ray fishes) are cartilaginous fishes of the order Batoidei, which are linked to sharks and belong to the Chondrichthyes class. This order includes 534 species.
Rays are differentiated from sharks by a flattened, disklike body, having five-gill openings and the mouth in general, located on the underside. Rays are further differentiated from the sharks by their wing-like and greatly enlarged pectoral fins, which extend forward along the sides of the head above the gill openings.
Several rays swim and breathe differently from sharks, propelling themselves with the pectoral fins and taking in water for respiration through large openings (which are spiracles) on the head's upper surface rather than via mouth. The tail of ray is generally long and slender and, in several species, bears either one or more sharp, saw-edged, venomous spines, which can be used to inflict painful wounds.
Predominantly, rays are marine and can be found in all oceans. Several are slow-moving bottom dwellers. Manta rays feed on small animals and plankton; others take different fishes and invertebrates, at times damaging commercially valuable shellfish beds. Aside from skates, all rays may or may not have lived young. Fertilization is internal, which is the male introducing sperm into the female by means of the special copulatory organs (called claspers), which are the modified edges of the pelvic fins.
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Classification of Types of Ray Fishes
Rays are classified into the following groups or the types of rays are given as sawfishes, electric rays, skates, including various families of rays, which have slender, whiplike tails equipped with spines and that are all-inclusively known as whip-tailed rays or stingrays.
The electric rays (suborder Torpedinoidei) are differentiated by large paired electric organs between the head and pectoral fins, with which they may give powerful shocks either for defensive purposes or to kill the prey. The electric rays have bare and smooth skin; the trunk and head create a circular disc with the pectoral fins, and the tail is sturdy and short. Up to 20 species are known to inhabit warm seas, with some of them reaching a weight of 200 pounds (90 kg).
All the other types of rays that lack electric organs, in general, have rough skin, often bearing strong spines. The sawfishes (the Pristidae family) have a snout, which is modified into a long blade possessing a series of strong teeth on every side. Up to six species are known from the warm seas, frequenting estuaries and sandy shores.
In the skates (with the suborder Rajoidei), the large pectoral fins extend to the snout and backward, stopping abruptly at the slender tail's base. Skates, unlike other rays, lay eggs that are big and oblong in shape, with leathery and black shells that have a tendril at every corner that allows them to attach to seaweed or other things. Skates lack the long, slender barbed spine, which differentiates stingrays. The most widespread skates belong to the genus Raja, which is the family Rajidae.
The rest of the rays comprise the suborder Myliobatoidei and have whip-tailed rays (Dasyatidae family), stingrays (Urolophidae), butterfly rays (Gymnuridae), manta rays (or devil rays; Mobulidae), eagle rays (Myliobatidae), and cow-nosed rays (Rhinopteridae).
Common to all these families' rays is a slender, long, whiplike tail that usually contains a barbed spine connected with the poison gland; this spine is capable of inflicting serious wounds, and it is a dangerous weapon when the tail gets lashes. Almost all these rays are inhabitants of warm seas, except for some species of Stingray, which live in the rivers of South America.
The guitarfishes are defined as a group of fishes, which are closely related to the rays and are either classified as a suborder (Rhinobatoidei) or as a separate order (Rhinobatiformes) of the ray order (Batoidei).
Batoids are flat-bodied, and they are cartilaginous marine fish, like sharks, which means that they carry a boneless skeleton made of elastic and tough cartilage. Most batoids hold five ventral slot-like body openings known as gill slits, which lead from the gills, but the Hexatrygonidae contains six. Batoid gill slits lie on the underside under the pectoral fins, whereas sharks lie on the sides of the head.
Most of the batoids have a flat, disklike body, with the exception of sawfishes and guitarfishes, while most of the sharks hold a spindle-shaped body. Several species of batoid have developed their pectoral fins into broad flat appendages, which are wing-like, and the anal fin is absent. The eyes and spiracles are situated on top of the head. Batoids hold a centrally located mouth and may considerably protrude their upper jaw (called palatoquadrate cartilage) away from the cranium to capture prey.
The jaws contain euhyostylic type suspension that relies totally on the hyomandibular cartilages for support. Bottom-dwelling batoids breathe by water intake in through the spiracles, rather than the mouth as most fishes do, and passing it outward via gills.
Batoids reproduce in numerous ways. Batoids undergo internal fertilization, as is characteristic of elasmobranchs. Internal fertilization is more advantageous to the batoids as it conserves sperm, doesn't expose eggs to consumption by predators, and ensures all the energy involved in reproduction is retained but not lost to the environment. All the skates and a few rays are oviparous (as egg-laying) while the other rays are ovoviviparous, which means that they give birth to young that develop in a womb but with no involvement of a placenta.
The oviparous' eggs skates are laid in leathery egg cases, which are commonly called mermaid's purses and which often wash up empty on the beaches in areas where the skates are common.
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When sharks and rays are fished, capture-induced preterm birth and abortion (together known as capture-induced parturition) occur often. Capture-induced parturition is very rarely considered in fisheries management despite being exhibiting to take place in at least 12% of live-bearing rays and sharks (88 species to date).
Most of the species live on the seafloor, in a wide range of geographical regions – primarily in coastal waters, although a few live in deep waters to at least 3,000 metres (9,800 feet). Most of the batoids contain a cosmopolitan distribution, preferring subtropical and tropical marine environments, although there are cold-water and temperate species. Only some species, like manta rays, live in the open sea, and only some live in freshwater (freshwater rays), while a few batoids can live in the estuaries and brackish bays.
Most of the batoids have developed heavy and rounded teeth for crushing the shells of bottom-dwelling species such as clams, snails, oysters, crustaceans, and a few fishes, depending on the species. Manta rays feed on the plankton.
Batoids belong to the cartilaginous fish's ancient lineage. Fossil denticles (with tooth-like scales in the skin) resembling those of chondrichthyans of today date at least as far back as the Ordovician, having the oldest unambiguous fossils of cartilaginous fish dating from the middle Devonian. A clade within this particular diverse family, the Neoselachii, emerged by the Triassic, with the best-understood neoselachian fossils dating from the Jurassic. The oldest confirmed ray is the Antiquaobatis, from the Pliensbachian of Germany. The clade is shown today by sharks, rays, sawfish, and skates.
Stingrays are a kind of cartilaginous fish that is linked to sharks. They can be classified in the suborder Myliobatoidei of the order Myliobatiformes and has eight families: Plesiobatidae (deepwater Stingray), Hexatrygonidae (sixgill Stingray), Urotrygonidae (round rays), Urolophidae (stingarees), Potamotrygonidae (river stingrays), Dasyatidae (whiptail stingrays), Gymnuridae (butterfly rays), and Myliobatidae (eagle rays).
Stingrays may be found in coastal subtropical and tropical marine environments all around the world. A few species, such as Dasyatis thetidis, are found in warmer temperate oceans, including others, such as Plesiobatis daviesi, which are found in the deep ocean. The river stingrays, and numerous whiptail stingrays (such as the Niger stingray), are restricted to freshwater. Most of the myliobatoids are demersal (inhabiting the next-to-lowest zone in the water column), but a few, such as the eagle rays and the pelagic Stingray, are pelagic.
Types of Stingrays
There are up to 220 known stingray species (types of stingrays), which are organized into 10 families and 29 genera. Stingray species are the ones, which are progressively becoming vulnerable or threatened to extinction, specifically as the consequence of unregulated fishing. As of 2013, 45 species have been listed as endangered or vulnerable by the IUCN. The status of a few other species is poorly known, leading to their being listed as data deficient.
Reproduction of Stingrays
During the breeding season, males of different stingray species, such as Urolophus halleri, can rely on their ampullae of Lorenzini to sense certain electrical signals given off by the mature females prior to the potential population. When a male is courting a female, it follows the female closely, biting at its pectoral disc. The male then places one of its two claspers into the female's valve.
Usually, stingrays are not aggressive and ordinarily attack humans only when provoked, such as when a ray is stepped on accidentally. Contact with the stinger will cause local trauma (from the cut itself), swelling, pain, muscle cramps from the venom, and later may result in the infection from fungi or bacteria. The injury is more painful but seldom life-threatening unless the stinger pierces a vital area. Usually, the barb breaks off in the wound, and surgery may be needed for the fragment removal.
Fatal stings are rarer. In 2006, the death of Steve Irwin was only the second recorded in the Australian waters since 1945. The stinger entered his heart and through his thoracic wall, causing significant damage and bleeding.