Temporal range: Early Triassic-Recent
|"Devil fish, Mobula mobular|
Batoidea is a "superorder of "cartilaginous fish commonly known as rays. They and their close relatives, the "sharks, comprise the subclass "Elasmobranchii. Rays are the largest group of cartilaginous fishes, with well over 600 species in 26 families. 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 spindle-shaped 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 fertilization. Internal fertilization 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.
Capture induced premature birth and abortion (collectively called capture-induced parturition) occurs frequently in sharks/rays when fished. Capture-induced parturition is rarely considered in fisheries management despite being shown to occur in at least 12% of live bearing sharks and rays (88 species to date).
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.
Most batoids 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.
|Phylogenetic tree of Batoidea["page needed]|
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 "Mesozoic "Sclerorhynchoidea are "basal or "incertae sedis; they show features of the Rajiformes but have snouts resembling those of sawfishes. However, evidence indicates they are probably the sister group to sawfishes
|"Myliobatiformes||""||"Stingrays and relatives||10||29||223||1||16||33||"Myliobatiformes include "stingrays, "butterfly rays, "eagle rays, and "manta rays. They were formerly included in the order "Rajiformes, but more-recent "phylogenetic studies have shown that they are a "monophyletic group, and that its more-"derived members evolved their highly flattened shapes independently of the "skates.|
|"Rajiformes||""||"Skates and relatives||5||36||270||4||12||26||"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.|
|"Torpediniformes||""||"Electric rays||4||12||69||2||9||The electric rays have "electric organs in their pectoral fin discs that generate "electric current. They are used to immobilize prey and for defense. The current is strong enough to stun humans, and the "ancient Greeks and "Romans used these fish to treat ailments such as "headaches.|
|"Rhinopristiformes||""||Shovelnose rays and relatives||1||2||5-7||3-5||2||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). All species of sawfish are endangered or critically endangered.|
* the placement of these families is uncertain
All sharks and rays are "cartilaginous fishes, "contrasting with bony fishes. Many rays are adapted for feeding on the bottom. "Guitarfishes are somewhat between sharks and rays, displaying characteristics of both (though they are classified as rays).
|Comparison of "sharks, "guitar fishes and rays|
|Shape||"laterally compressed spindle||"dorsoventrally compressed (flattened) disc||"dorsoventrally compressed (flattened) disc|
|"Spiracles||not always present||always present|
|Habitat||usually "pelagic surface feeders, though "carpet sharks are "demersal "bottom feeders||demersal/pelagic mix||usually demersal bottom feeders|
|Eyes||usually at the side of the head||usually on top of the head||usually on top of the head|
|"Gill openings||on the sides||ventral (underneath)|
|"Pectoral fins||distinct||not distinct||not distinct|
|Tail||large "caudal fin used for propulsion||"caudal fin that can be used for propulsion||varies from thick tail as extension of body to a whip that can sting to almost no tail.|
|"Locomotion||swim by moving their "caudal (tail) fin from side to side||Guitar fish and "sawfish have a caudal fin like the shark.||swim by flapping their pectoral fins like wings.|
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