Difference between revisions of "Ray" - New World Encyclopedia

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In [[zoology]], '''ray''' is the common name for [[Chondrichthyes|cartilaginous fish]] comprising the order ''Rajiformes'' (or [[Batoidea]]), characterized by enlarged and flat pectoral fins continuous with the head, no anal fin, eyes on the dorsal surface, and a narrow tail. The [[skate]]s comprise a family, Rajidae, within the Rajiformes, and thus can be considered a type of ray. For those taxonomic systems recognizing Batoidea as a superorder, ray may also be used as a term for members of this superorder.
  
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'''Rajiformes''' is the order of '''true rays''' and [[skate]]s, flat-bodied [[Chondrichthyes|cartilaginous fishes]] related to [[shark]]s.
+
Rays provide various ecological, culinary, and aesthetic values. [[Ecology|Ecologically]], rays are important in [[food chain]]s, consuming [[mollusk]]s ([[snail]]s, clams, oysters), [[crustacean]]s, small fish, and even [[plankton]] (in the case of manta rays), while being consumed by [[shark]]s, among other predators. Some rays are eaten by people, with the large pectoral fins being edible. Aesthetically, rays with their unique form and undulating movements add to the wonder of [[nature]] and are popular attractions in public aquariums.
 +
 
 +
However, there is concern that certain ray [[species]] are vulnerable to overfishing as they are sought for [[food]], particularly given that they tend to be characterized by slow growth, low reproductive rates, and high age at maturity (MCS 2007). The Marine Conservation Society recommends that consumers avoid eating rays unless certain they are one of the smaller ray species (spotted, cuckoo, or starry rays) whose populations are relatively stable and that individuals not be eaten below the size at which the species matures (MCS 2007). On the other hand, there also is concern that overfishing of sharks in some areas has led to an increase in particular ray populations, such as the cownose rays, and as a consequence this might be endangering the scallop populations, which are being eaten by the rays (Schmid 2007).  
  
 
==Overview==
 
==Overview==
−
The ''[[Chondrichthyes]]'' or "cartilaginous fishes" are jawed [[fish]] with paired fins, paired nostrils, scales, two-chambered [[heart]]s, 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.
+
The ''[[Chondrichthyes]]'' or "cartilaginous fishes" are jawed [[fish]] with paired fins, paired nostrils, scales, two-chambered [[heart]]s, 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).  
  
−
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.
+
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.
  
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==Batoidea==
+
There are diverse taxonomies, and Batoidea is variously considered a superorder (eg., Taxonomicon 2007; Frisk et al. 2005; Systema Naturae 2000 2007; Rocco et al. 2007) or an order (ITIS 2007; Froese and Pauly 2005; Myers et al. 2006). As a superorder, Batoidea typically includes three orders: Rajiformes (true rays), Torpediniformes (electric rays), and Pristiformes (sawfishes). Some recognize additional orders such as [[Myliobatiformes]] ([[eagle ray]]s) and Rhinobatiformes ([[guitarfish]]es). On the other hand, Nelson (1994) recognizes the sawfishes, electric rays, and guitarfishes as families under the order Rajiformes.
  
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{{Taxobox
+
==Description==
−
| color = pink
 
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| name = Batoidea
 
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| image = spotted_eagle_ray.jpg
 
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| image_width = 250px
 
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| image_caption = [[Spotted eagle ray]], ''Aetobatus narinari''
 
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| regnum = [[Animal]]ia
 
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| phylum = [[Chordate|Chordata]]
 
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| classis = [[Chondrichthyes]]
 
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| subclassis = [[Elasmobranchii]]
 
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| superordo = '''Batoidea'''
 
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| subdivision_ranks = [[Order (biology)|Order]]s
 
−
| subdivision =
 
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[[Rajiformes]] - common rays and [[skate]]s<br/>
 
−
[[Pristiformes]] - [[sawfish (fish)|sawfish]]es<br/>
 
−
[[Torpediniformes]] - [[electric ray]]s<br/>
 
−
See text for families.
 
−
}}
 
  
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'''Batoidea''' is a [[superorder]] of [[Chondrichthyes|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 [[stingray]]s, [[skate]]s, [[electric ray]]s, [[guitarfish]]es and [[sawfish]]es.
+
True rays, including [[skate]]s, are placed in the order Rajiformes. Members of Rajiformes are characterized by the anterior edge of the pectoral fin, which is greatly enlarged, being attached to the side of the head anterior to the gill openings (Nelson 1994). They also have ventral gill openings, 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. In addition, members of Rajiformes lack an anal fin and lack a nictitating membrane with the cornea attached directly to the skin around the eyes (Nelson 1994).  
  
−
Batoids are most closely related to [[shark]]s 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.{{Fact|date=February 2007}}<!-- No mention of this in the catshark article which is emphatic that they are sharks. —>
+
Like sharks, rays are [[cartilage|cartilaginous]] marine fish, which means their skeleton is characterized by rubbery cartilage, which is very light and flexible, rather than [[bone]], as in the [[Osteichthyes|bony fish]]es (class Osteichthyes (such as [[cod]] or [[salmon]])). As with other chondrichthyans, rays have [[jaw]]s, paired [[fin]]s, paired nostrils, scales, and two-chambered [[heart]]s.
  
−
Batoids are flat-bodied, and, like sharks, are a species of [[cartilage|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 fin]]s 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 [[guitarfish]]es and [[sawfish (fish)|sawfishes]], while most sharks have a streamlined body. Many species of batoid have developed their pectoral fins into broad flat wing-like appendages.
+
Rays 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 fin]]s on the underside, whereas a shark's are on the sides of the head. Most rays have a flat, disk-like body, with the exception of the [[guitarfish]]es and [[sawfish (fish)|sawfishes]], while most sharks have a streamlined body.  
  
−
The eyes and [[spiracle]]s are located on top of the head.
+
Most rays give birth to live young ([[Ovoviviparity|ovoviviparous]]), but the skates in family Rajidae are characterized by eggs that are encased in a horny capsule with four long tips (Nelson 1994).
  
−
Batoid eggs, unlike those of most other fishes, are fertilized inside the female's body. The eggs of all batoids except for the [[skate]]s (family [[Rajidae]]) hatch inside the female and are born alive ([[Ovoviviparity|ovoviviparous]]). Female skates lay internally fertilized flat, rectangular, leathery-shelled eggs, with [[tendril]]s 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&mdash;many in coastal waters, few live in deep waters. Only a few species, like [[manta ray]]s, live in the open sea, and only a few live in freshwater. Some rays can live in brackish bays and estuaries. Bottom-dwelling rays breathe by taking water in through the [[spiracle]]s, rather than through the mouth as most fishes do, and pass it outward through the gills.
  
−
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 ray]]s, 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 [[spiracle]]s, rather than through the mouth as most fishes do, and passing it outward through the gills.
+
Members of Rajiformes tend to have pavementlike teeth (Nelson 1994). The heavy, rounded teeth are useful for crushing the shells of bottom-dwelling species such as [[snails]], [[clams]], [[oysters]], [[crustacean]]s, and some [[fish]], depending on the species. [[Manta ray]]s feed on [[plankton]].
  
−
Most batoids have developed heavy, rounded teeth for crushing the shells of bottom-dwelling species such as [[snails]], [[clams]], [[oysters]], [[crustacean]]s, and some [[fish]], depending on the species. [[Manta ray]]s feed on [[plankton]].
+
==Classification==
−
 
 
−
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 ray]]s and their relatives; Rhinobatiformes, containing the [[guitarfish]]es (which may be further split into Rhynchobatiformes, containing the [[shovelnosed guitarfish]]es, and Rhiniformes, the [[sharkfin guitarfish]]es).
 
−
 
 
−
===Order Rajiformes (true rays)===
 
−
[[Image:Ray.jpg|300px|thumb|right|Ray]]
 
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* Family [[Anacanthobatidae]] ([[smooth skate]]s)
 
−
* Family [[Dasyatidae]] ([[stingray]]s). 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 ray]]s)
 
−
* Family [[Hexatrygonidae]] ([[sixgill stingray]]s)
 
−
* Family [[Myliobatidae]] ([[eagle ray]]s). The largest of rays, including the giant [[manta ray]]s. Most eagle rays have one poison-carrying spine.
 
−
* Family [[Plesiobatidae]] ([[deepwater stingray]]s)
 
−
* Family [[Potamotrygonidae]] ([[river stingray]]s)
 
−
* Family [[Rajidae]] ([[skate]]s)
 
−
* Family [[Rhinobatidae]] ([[guitarfish]]es). They have a body structure similar that of the sawfishes, but are not thought to be closely related.
 
−
* Family [[Urolophidae]] ([[round ray]]s)
 
−
 
 
−
===Order Pristiformes (sawfishes) ===
 
−
Sawfishes are shark-like in form, having tails used for swimming and smaller [[pectoral fin]]s 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 [[Organ (anatomy)|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]]
 
  
 +
Nelson (1994) recognizes four suborders, 12 families, 62 genera, and about 456 species in Rajiformes. He give the following classification for the order Rajiformes:
  
 +
*''Rajiformes''
 +
**Superorder Pristidae
 +
***Family Pristidae (sawfishes)
 +
**Superorder Torpedinoidei
 +
***Family Torpedinidae (electric rays)
 +
***Family Narcinidae
 +
**Superorder Rajoidei
 +
***Family Rhinidae
 +
***Family Rhinobatidae (guitarfishes)
 +
***Family Rajidae (skates)
 +
**Superorder Myliobatoidei
 +
***Family Plesiobatidae (deepwater stingray)
 +
***Family Hexatrygonidae
 +
***Family Dasyatidae (stingrays)
 +
***Family Urolophidae (round stingrays)
 +
***Family Gymnuridae (butterfly rays)
 +
***Family Myliobatidae (eagle rays)
  
−
==Classification==
+
In this classification by Nelson, he recognizes the four orders of Compagno (1973) as suborders. Compagno recognizes Batoidea as a superorder
−
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 ray]]s and their relatives; Rhinobatiformes, containing the [[guitarfish]]es (which may be further split into Rhynchobatiformes, containing the [[shovelnosed guitarfish]]es, and Rhiniformes, the [[guitarfish]]es).
 
−
 
 
−
* [[Anacanthobatidae]] ([[smooth skate]]s)
 
−
* [[Dasyatidae]] ([[stingray]]s). 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 ray]]s)
 
−
* [[Hexatrygonidae]] ([[sixgill stingray]]s)
 
−
* [[Myliobatidae]] ([[eagle ray]]s). The largest of rays, including the giant [[manta ray]]s. Most eagle rays have one poison-carrying spine.
 
−
* [[Plesiobatidae]] ([[deepwater stingray]]s)
 
−
* [[Potamotrygonidae]] ([[river stingray]]s)
 
−
* [[Rajidae]] ([[skate]]s)
 
−
* [[Rhinobatidae]] ([[guitarfish]]es). They have a body structure similar that of the [[sawfish (fish)|sawfishes]], but are not thought to be closely related.
 
−
* [[Urolophidae]] ([[round ray]]s)
 
  
 
==References==
 
==References==
−
{{commonscat|Rajiformes}}
 
−
* {{FishBase order | order = Rajiformes | month = January | year = 2006}}
 
−
* [http://www.elasmo-research.org/education/shark_profiles/batoids.htm 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.
 
−
 
−
 
−
* [http://www.elasmo-research.org/education/shark_profiles/batoids.htm 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.
 
  
 +
* Compagno, L. J. V. 1973. Interrelationships of living elasmobranhs. In P. H. Greenwood, R. S. Miles, and C. Patterson, eds. ''Interrelationships of fishes''. ''J. Linn. Soc. (Zool.) 53 (Suppl. 1): 15-61.
 +
* Frisk, M. G., T. J. Miller, and N. K. Dulvy. 2005. [http://journal.nafo.int/35/frisk/4-frisk.html Life histories and vulnerability to exploitation of elasmobranchs: Inferences from elasticity, perturbation and phylogenetic analyses] ''J. Northw. Atl. Fish. Sci.'' 35: 27-45. Retrieved January 3, 2008.
 +
* Froese, R. and D. Pauly, eds. 2005. [http://www.fishbase.org/Summary/OrdersSummary.cfm?order=Rajiformes Order Rajiformes] ''FishBase'. Retrieved January 3, 2008.
 +
* Integrated Taxonomic Information System (ITIS). 2007. [http://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=563992 Batoidea Taxonomic Serial No.: 563992] ''ITIS Report''. Retrieved January 3, 2008.
 +
* Marine Conservation Society (MCS). 2007. [http://www.fishonline.org/advice/avoid/?item=35 Fish to avoid: Skates and rays] ''Marine Conservation Society''. Retrieved January 3, 2008.
 +
* McEachran, J. D., K. A. Dunn, and T. Miyake. 1996. Interrelationships of the batoid fishes (Chondrichthyes: Batoidea). In M. L. J. Stiassny, L. R. Parenti, and G. David Johnson, ''Interrelationships of Fishes''. San Diego: Academic Press. ISBN 0126709505.
 +
* Myers, P., R. Espinosa, C. S. Parr, T. Jones, G. S. Hammond, and T. A. Dewey. 2006. [http://animaldiversity.ummz.umich.edu/site/accounts/classification/Rajiformes.html Rajiformes]. ''The Animal Diversity Web'' (online). Retrieved December 18, 2007.
 +
* Nelson, J. S. 1994. ''Fishes of the World.'' New York: John Wiley and Sons. ISBN 0471547131.
 +
* Rocco, L, I. Liguori, D. Costagliola, et al. 2007. [http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6T39-4M22067-6&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=0cdf2112451e761678ffbfeb28dfe269 Molecular and karyological aspects of Batoidea (Chondrichthyes, Elasmobranchi) phylogeny] ''Gene'' 389(1): 80-86. Retrieved January 3, 2008.
 +
* 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.
 +
* Systema Naturae 2000. 2007. Superorder Batoidea ''Systema Naturae 2000''.
 +
* Taxonomicon. 2007. [http://www.taxonomy.nl/Taxonomicon/TaxonTree.aspx?id=42011 Superorder Batoidea] ''Taxonomicon''. Retrieved January 3, 2008.
  
 
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Latest revision as of 19:06, 16 April 2023

Rajiformes
Spotted eagle ray, Aetobatus narinari
Spotted eagle ray, Aetobatus narinari
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Subclass: Elasmobranchii
Superorder: Batoidea
Order: Rajiformes
Families

Anacanthobatidae
Dasyatidae
Gymnuridae
Hexatrygonidae
Myliobatidae
Plesiobatidae
Potamotrygonidae
Rajidae
Rhinobatidae
Urolophidae

In zoology, ray is the common name for cartilaginous fish comprising the order Rajiformes (or Batoidea), characterized by enlarged and flat pectoral fins continuous with the head, no anal fin, eyes on the dorsal surface, and a narrow tail. The skates comprise a family, Rajidae, within the Rajiformes, and thus can be considered a type of ray. For those taxonomic systems recognizing Batoidea as a superorder, ray may also be used as a term for members of this superorder.

Rays provide various ecological, culinary, and aesthetic values. Ecologically, rays are important in food chains, consuming mollusks (snails, clams, oysters), crustaceans, small fish, and even plankton (in the case of manta rays), while being consumed by sharks, among other predators. Some rays are eaten by people, with the large pectoral fins being edible. Aesthetically, rays with their unique form and undulating movements add to the wonder of nature and are popular attractions in public aquariums.

However, there is concern that certain ray species are vulnerable to overfishing as they are sought for food, particularly given that they tend to be characterized by slow growth, low reproductive rates, and high age at maturity (MCS 2007). The Marine Conservation Society recommends that consumers avoid eating rays unless certain they are one of the smaller ray species (spotted, cuckoo, or starry rays) whose populations are relatively stable and that individuals not be eaten below the size at which the species matures (MCS 2007). On the other hand, there also is concern that overfishing of sharks in some areas has led to an increase in particular ray populations, such as the cownose rays, and as a consequence this might be endangering the scallop populations, which are being eaten by the rays (Schmid 2007).

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.

There are diverse taxonomies, and Batoidea is variously considered a superorder (eg., Taxonomicon 2007; Frisk et al. 2005; Systema Naturae 2000 2007; Rocco et al. 2007) or an order (ITIS 2007; Froese and Pauly 2005; Myers et al. 2006). As a superorder, Batoidea typically includes three orders: Rajiformes (true rays), Torpediniformes (electric rays), and Pristiformes (sawfishes). Some recognize additional orders such as Myliobatiformes (eagle rays) and Rhinobatiformes (guitarfishes). On the other hand, Nelson (1994) recognizes the sawfishes, electric rays, and guitarfishes as families under the order Rajiformes.

Description

True rays, including skates, are placed in the order Rajiformes. Members of Rajiformes are characterized by the anterior edge of the pectoral fin, which is greatly enlarged, being attached to the side of the head anterior to the gill openings (Nelson 1994). They also have ventral gill openings, 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. In addition, members of Rajiformes lack an anal fin and lack a nictitating membrane with the cornea attached directly to the skin around the eyes (Nelson 1994).

Like sharks, rays are cartilaginous marine fish, which means their skeleton is characterized by rubbery cartilage, which is very light and flexible, rather than bone, as in the bony fishes (class Osteichthyes (such as cod or salmon)). As with other chondrichthyans, rays have jaws, paired fins, paired nostrils, scales, and two-chambered hearts.

Rays 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 rays have a flat, disk-like body, with the exception of the guitarfishes and sawfishes, while most sharks have a streamlined body.

Most rays give birth to live young (ovoviviparous), but the skates in family Rajidae are characterized by eggs that are encased in a horny capsule with four long tips (Nelson 1994).

Most species live on the sea floor, in a variety of geographical regions—many in coastal waters, few live in deep waters. Only a few species, like manta rays, live in the open sea, and only a few live in freshwater. Some rays can live in brackish bays and estuaries. Bottom-dwelling rays breathe by taking water in through the spiracles, rather than through the mouth as most fishes do, and pass it outward through the gills.

Members of Rajiformes tend to have pavementlike teeth (Nelson 1994). The heavy, rounded teeth are useful 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.

Classification

Nelson (1994) recognizes four suborders, 12 families, 62 genera, and about 456 species in Rajiformes. He give the following classification for the order Rajiformes:

  • Rajiformes
    • Superorder Pristidae
      • Family Pristidae (sawfishes)
    • Superorder Torpedinoidei
      • Family Torpedinidae (electric rays)
      • Family Narcinidae
    • Superorder Rajoidei
      • Family Rhinidae
      • Family Rhinobatidae (guitarfishes)
      • Family Rajidae (skates)
    • Superorder Myliobatoidei
      • Family Plesiobatidae (deepwater stingray)
      • Family Hexatrygonidae
      • Family Dasyatidae (stingrays)
      • Family Urolophidae (round stingrays)
      • Family Gymnuridae (butterfly rays)
      • Family Myliobatidae (eagle rays)

In this classification by Nelson, he recognizes the four orders of Compagno (1973) as suborders. Compagno recognizes Batoidea as a superorder

References
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