Ray
| Rajiformes | ||||||||||||
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 Spotted eagle ray, Aetobatus narinari
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Anacanthobatidae |
Rajiformes is the order of true rays and skates, flat-bodied cartilaginous fishes related to sharks.
note: In zoology, skate is the common name for cartilaginous fish belonging to the family Rajidae in the superorder Batoidea of rays, characterized by enlarged and flat pectoral fins continuous with the head, no anal fin, two dorsal fins, and a very slender, spineless tail.
Overview
The Chondrichthyes or "cartilaginous fishes" are jawed fish with paired fins, paired nostrils, scales, two-chambered hearts, and skeletons made of cartilage rather than bone. They are divided into two subclasses: Elasmobranchii (sharks, rays, and skates) and Holocephali (chimaera, sometimes called ghost sharks). The Elasmobranchii are sometimes divided into two superorders, Selachimorpha (sharks) and Batoidea or Batidoidimorpha (rays, skates, sawfish). Nelson (1994) notes that there is growing acceptance of the view that sharks and rays together form a monophyletic group (superorder Euselachii), and sharks without rays are a paraphyletic group.
Rays, including skates, are placed in the order Rajiformes of the superorder Batoidea (or superorder Euselachii with the sharks). Members of Batoidea are characterized by ventral gill openings, and the anterior edge of the pectoral fin, which is greatly enlarged, is attached to the side of the head anterior to the gill openings (Nelson 1994). Members of Rajiformes also lack an anal fin and the eyes and spiracles are on the dorsal surface (Nelson 1994). The body is normally strongly depressed and in most water for breathing is taken in through the spiracle rather than the mouth.
Batoidea
| Batoidea | ||||||||||
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Spotted eagle ray, Aetobatus narinari
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Rajiformes - common rays and skates |
Batoidea is a superorder of cartilaginous fish containing more than 500 described species in thirteen families. They are commonly known as rays, but that term is also used specifically for batoids in the order Rajiformes, the "true rays". Batoids include stingrays, skates, electric rays, guitarfishes and sawfishes.
Batoids are most closely related to sharks and young batoids look very much like young sharks. Indeed according to recent DNA analyses the catshark is more closely related to the batoids than to other sharks.[citation needed]
Batoids 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. Batoids also are like sharks in having slot-like body openings called gill slits that lead from the gills. 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 eyes and spiracles are located on top of the head.
Batoid eggs, unlike those of most other fishes, are fertilized inside the female's body. The eggs of all batoids except for the skates (family Rajidae) hatch inside the female and are born alive (ovoviviparous). 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.
Most species live on the sea floor, in a variety of geographical regions - many in coastal waters, few live in deep waters, most batoids have a somewhat cosmopolitan distribution, in tropical and subtropical marine environments, temperate or cold-water species. Only a few species, like manta rays, live in the open sea, and only a few live in freshwater. Some batoids can live in brackish bays and estuaries. 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.
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.
The classification of batoids is currently undergoing revision. This article follows FishBase in dividing batoids into three orders. Some taxonomists argue in favour of placing all batoids in a single order, Rajiformes; others propose a division into five or six orders. The additional orders in these systems are Myliobatiformes, containing the eagle rays and their relatives; Rhinobatiformes, containing the guitarfishes (which may be further split into Rhynchobatiformes, containing the shovelnosed guitarfishes, and Rhiniformes, the sharkfin guitarfishes).
Order Rajiformes (true rays)
- Family Anacanthobatidae (smooth skates)
- Family Dasyatidae (stingrays). Named for the venomous spines along the tail; these contain a poison that causes pain and may cause symptoms such as nausea, vomiting, fever, chills, muscle cramps, tremors, paralysis, fainting, seizures, elevated heart rate, and decreased blood pressure (depending on the species). In addition, some species' toxins can be fatal to humans.
- Family Gymnuridae (butterfly rays)
- Family Hexatrygonidae (sixgill stingrays)
- Family Myliobatidae (eagle rays). The largest of rays, including the giant manta rays. Most eagle rays have one poison-carrying spine.
- Family Plesiobatidae (deepwater stingrays)
- Family Potamotrygonidae (river stingrays)
- Family Rajidae (skates)
- Family Rhinobatidae (guitarfishes). They have a body structure similar that of the sawfishes, but are not thought to be closely related.
- Family Urolophidae (round rays)
Order Pristiformes (sawfishes)
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 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).
- Family Pristidae
Order Torpediniformes (electric rays)
Electric rays 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.
- Family Narcinidae
- Family Torpedinidae
Classification
There are several proposed classifications of fish in the superorder Batoidea. In some classifications the order Rajiformes is split into two or three orders, the additional orders being Myliobatiformes, containing the eagle rays and their relatives; Rhinobatiformes, containing the guitarfishes (which may be further split into Rhynchobatiformes, containing the shovelnosed guitarfishes, and Rhiniformes, the guitarfishes).
- Anacanthobatidae (smooth skates)
- Dasyatidae (stingrays). Named for the venomous spines along the tail; these contain a poison that causes pain and may cause symptoms such as nausea, vomiting, fever, chills, muscle cramps, tremors, paralysis, fainting, seizures, elevated heart rate, and decreased blood pressure (depending on the species). In addition, some species' toxins can be fatal to humans.
- Gymnuridae (butterfly rays)
- Hexatrygonidae (sixgill stingrays)
- Myliobatidae (eagle rays). The largest of rays, including the giant manta rays. Most eagle rays have one poison-carrying spine.
- Plesiobatidae (deepwater stingrays)
- Potamotrygonidae (river stingrays)
- Rajidae (skates)
- Rhinobatidae (guitarfishes). They have a body structure similar that of the sawfishes, but are not thought to be closely related.
- Urolophidae (round rays)
ReferencesISBN links support NWE through referral fees
- "Rajiformes". FishBase. Ed. Ranier Froese and Daniel Pauly. January 2006 version. N.p.: FishBase, 2006.
- Batoids: Sawfishes, Guitarfishes, Electric Rays, Skates, and Sting Rays
- J. D. McEachran, K. A. Dunn, T. Miyake (1996). "Interrelationships of the batoid fishes (Chondrichthyes: Batoidea)". In Interrelationships of Fishes, Academic Press.
- Batoids: Sawfishes, Guitarfishes, Electric Rays, Skates, and Sting Rays
- J. D. McEachran, K. A. Dunn, T. Miyake (1996). "Interrelationships of the batoid fishes (Chondrichthyes: Batoidea)". In Interrelationships of Fishes, Academic Press.
- Froese, R. and D. Pauly. (Eds.). 2004. Family Rajidae: Skates. FishBase'. Retrieved December 14, 2007.
- Herbst, S. T. 2001. The New Food Lover's Companion: Comprehensive Definitions of Nearly 6,000 Food, Drink, and Culinary Terms. Barron's Cooking Guide. Hauppauge, NY: Barron's Educational Series. ISBN 0764112589.
- Marine Conservation Society. 2007. Fish to avoid: Skates and rays. Marine Conservation Society. Retrieved December 14, 2007.
- Murch, A. 2007. Shark taxonomy. Elasmodiver. Retrieved December 14, 2007.
- Nelson, J. S. 1994. Fishes of the World. New York: John Wiley and Sons. ISBN 0471547131.
- Schmid, R. E. 2007. Shark deaths upset rest of food chain: Shark overfishing may be endangering scallop populations, say scientists. Associated Press/ABCNews May 29, 2007. Retrieved December 14, 2007.
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