Batoidea is a superorder of cartilaginous fish commonly known as batoids or rays, but it also includes the skates and sawfishes. Approximately 560 species are described in thirteen families. Batoids are in the fish subclass Elasmobranchii along with sharks, as they are closely related. Rays are distinguished by their flattened bodies, enlarged pectoral fins that are fused to the head, and gill slits that are placed on their ventral surfaces.
Batoids are flat-bodied, and, like sharks, are cartilaginous marine fish, meaning they have a boneless skeleton made of a tough, elastic substance. Most batoids have five ventral slot-like body openings called gill slits that lead from the gills, but the Hexatrygonidae have six. Batoid gill slits lie under the pectoral fins on the underside, whereas a shark's are on the sides of the head. Most batoids have a flat, disk-like body, with the exception of the guitarfishes and sawfishes, while most sharks have a streamlined body. Many species of batoid have developed their pectoral fins into broad flat wing-like appendages. The anal fin is absent. The eyes and spiracles are located on top of the head. Batoids have a ventrally located mouth and can considerably protrude their upper jaw (palatoquadrate cartilage) away from the cranium to capture prey. The jaws have euhyostylic type suspension, which relies completely on the hyomandibular cartilages for support. Bottom-dwelling batoids breathe by taking water in through the spiracles, rather than through the mouth as most fishes do, and passing it outward through the gills.
Batoids reproduce in a number of ways. As is characteristic of elasmobranchs, batoids undergo internal fertilisation. Internal fertilisation is advantageous to batoids as it conserves sperm, does not expose eggs to consumption by predators, and ensures that all the energy involved in reproduction is retained and not lost to the environment. All skates and some rays are oviparous (egg laying) while other rays are ovoviviparous, meaning that they give birth to young which develop in a womb but without involvement of a placenta.
The eggs of oviparous skates are laid in leathery egg cases that are commonly known as mermaid's purses and which often wash up empty on beaches in areas where skates are common.
Most species live on the sea floor, in a variety of geographical regions — mainly in coastal waters, although some live in deep waters to at least 3,000 metres (9,800 ft). Most batoids have a cosmopolitan distribution, preferring tropical and subtropical marine environments, although there are temperate and cold-water species. Only a few species, like manta rays, live in the open sea, and only a few live in freshwater, while some batoids can live in brackish bays and estuaries.
The classification of batoids is currently undergoing revision; however, molecular evidence refutes the hypothesis that skates and rays are derived sharks. Nelson's 2006 Fishes of the World recognizes four orders. The MesozoicSclerorhynchoidea are basal or incertae sedis; they show features of the Rajiformes but have snouts resembling those of sawfishes.
Rajiformes include skates, guitarfishes, and wedgefishes. They are distinguished by the presence of greatly enlarged pectoral fins, which reach as far forward as the sides of the head, with a generally flattened body. The undulatory pectoral fin motion diagnostic to this taxon is known as rajiform locomotion. The eyes and spiracles are located on the upper surface of the body, and the gill slits on the underside. They have flattened, crushing teeth, and are generally carnivorous. Most species give birth to live young, although some lay eggs inside a protective capsule or mermaid's purse.
All sawfish species are endangered or critically endangered 
The sawfishes are shark-like in form, having tails used for swimming and smaller pectoral fins than most batoids. The pectoral fins are attached above the gills as in all batoids, 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 1.8 metres (6 ft) long, and 30 centimetres (1 ft) wide, and are used for slashing and impaling small fishes and to probe in the mud for embedded animals. Sawfishes can enter freshwater rivers and lakes. Some species reach a total length of 6 metres (20 ft).
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^"Reproduction overall". Skates and rays of Atlantic Canada. Canadian Shark Research Lab, Bedford Institute of Oceanography & Marine Fish Species, Risk Section, Northwest Atlantic Fisheries Center. Retrieved 27 May 2012.