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Torpediniformes |
| Electric rays | ||||||||||||
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 Blackspotted torpedo, Torpedo fuscomaculata
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The electric rays are a group of rays, flattened cartilaginous fish with enlarged pectoral fins, that comprise the order Torpediniformes. They are known for being capable of producing an electric discharge, ranging from as little as 8 volts up to 220 volts depending on species, used to stun prey and for defense.1 There are 69 species in four families.
Perhaps the most known members are those of the genus Torpedo, also called crampfish and numbfish, after which the device called a torpedo is named. The name comes from the Latin "torpere", to be stiffened or paralyzed, referring to the effect on someone who handles or steps on a living electric ray.
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Electric rays have a rounded pectoral disc with two moderately large rounded-angular (not pointed or hooked) dorsal fins (reduced in some narkids), and a stout, muscular tail with a well-developed caudal fin. The body is thick and flabby, with soft, loose skin devoid of dermal denticles and thorns. A pair of kidney-shaped electric organs are found at the base of the pectoral fins. The snout is broad, large in the Narcinidae but reduced in all other families. The mouth, nostrils, and five pairs of gill slits are located underneath the disc.12
The electrogenic properties of electric rays have been known since antiquity. The ancient Greeks used electric rays to numb the pain of childbirth and operations, calling the fish narke, meaning "paralysis".1 Scribonius Largus, a Roman physician, recorded the use of torpedo fish for treatment of headaches and gout in his Compositiones Medicae of 46 AD.3
The four families of the Torpediniformes are typically grouped into two superfamilies: Hypnidae and Torpedinidae in the Torpedinoidea, and Narkidae and Narcinidae in the Narcinoidea. The Torpedinoidea specialize on large prey, which are stunned using their electric organs and swallowed whole, while the Narcinoidea specialize on small prey on or in the bottom substrate. Both groups use electricity for defense, but it is unclear whether the Narcinoidea use electricity in feeding.4
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