Batoidea is a superorder of
cartilaginous fishChondrichthyes or cartilaginous fishes are jawed fish with paired fins, paired nares, scales, two-chambered hearts, and skeletons made of cartilage rather than bone...
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
RajiformesRajiformes is the order of true rays and skates, flat-bodied cartilaginous fishes related to sharks.Rajiforms 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...
, the "true rays". Batoids include
stingrayThe stingrays are a family—Dasyatidae—of rays, cartilaginous fishes related to sharks. They are common in coastal tropical and subtropical marine waters throughout the world, but the family also includes species found in warmer temperate oceans such as Dasyatis thetidis, and species entirely...
s,
skateSkates are cartilaginous fish belonging to the family Rajidae in the superorder Batoidea of rays. There are more than 200 described species in 27 genera.-Description and habitat:...
s,
electric rayThe 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...
s,
guitarfishThe guitarfish are a family, Rhinobatidae, of rays. The guitarfish are known for an elongated body with a flattened head and trunk and small ray like wings. The combined range of the various species is tropical, subtropical and temperate waters worldwide...
es and
sawfishSawfishes are a family of marine animals related to rays. Their most stunning appearance is a long, toothy snout. They are members of the sole living family Pristidae within the order Pristiformes, from the Greek pristēs meaning "a sawyer" or "a saw"...
es.
Anatomy
Batoids are flat-bodied, and, like sharks, are a species of
cartilaginous marine fishChondrichthyes or cartilaginous fishes are jawed fish with paired fins, paired nares, scales, two-chambered hearts, and skeletons made of cartilage rather than bone...
, meaning they have a boneless
skeletonIn biology, a skeleton is a rigid framework that provides protection and structure in many types of animal, particularly those of the phylum Chordata and of the superphylum Ecdysozoa. Exoskeletons are external, as is typical of many invertebrates; they enclose the soft tissues and organs of the...
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
guitarfishThe guitarfish are a family, Rhinobatidae, of rays. The guitarfish are known for an elongated body with a flattened head and trunk and small ray like wings. The combined range of the various species is tropical, subtropical and temperate waters worldwide...
es 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
spiracleSpiracles are small openings on the surface of some animals that usually lead to respiratory systems.In elasmobranchs , a spiracle is found behind each eye, and is often used to pump water through the gills while the animal is at rest .-Spiracles in insects:Insects and some more advanced spiders...
s are located on top of the head.
Habitat
Most species live on the sea floor, in a variety of geographical regions - many in coastal waters, few live in deep waters to at least , most batoids have a somewhat
cosmopolitan distributionIn biogeography, cosmopolitan distribution is a state of being found almost anywhere around the world. A cosmopolitan biological category, e.g. genus, may be called a cosmopolite.Examples of cosmopolitan species:* Humans* House dust mite...
, in tropical and subtropical marine environments, temperate or cold-water species. Only a few species, like
manta rayThe manta ray , is the largest of the rays. The largest known specimen was more than across, with a weight of about . It ranges throughout tropical waters of the world, typically around coral reefs...
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
spiracleSpiracles are small openings on the surface of some animals that usually lead to respiratory systems.In elasmobranchs , a spiracle is found behind each eye, and is often used to pump water through the gills while the animal is at rest .-Spiracles in insects:Insects and some more advanced spiders...
s, rather than through the mouth as most fishes do, and passing it outward through the gills.
Feeding
Most batoids have developed heavy, rounded teeth for crushing the shells of bottom-dwelling species such as snails,
clamsCLaMS is a modular chemistry transport model system developed at Research Centre Jülich, Germany. CLaMS was first described by McKenna et al. and was expanded into three dimensions by Konopka et al....
, oysters,
crustaceanCrustaceans are a very large group of arthropods, comprising almost 52,000 described species , and are usually treated as a subphylum . They include various familiar animals, such as crabs, lobsters, crayfish, shrimp, krill and barnacles...
s, and some
fishA fish is any aquatic vertebrate animal that is typically ectothermic , covered with scales, and equipped with two sets of paired fins and several unpaired fins...
, depending on the species.
Manta rayThe manta ray , is the largest of the rays. The largest known specimen was more than across, with a weight of about . It ranges throughout tropical waters of the world, typically around coral reefs...
s feed on
planktonPlankton consist of any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. Plankton are defined by their ecological niche rather than their phylogenetic or taxonomic classification...
.
Classification
The classification of batoids is currently undergoing revision. This article follows
FishBaseFishBase is a comprehensive database of information about fish. , it included descriptions of over 30,000 species, over 260,000 common names in hundreds of languages, over 46,000 pictures, and references to more than 42,000 works in the scientific literature....
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
MyliobatiformesMyliobatiformes Compagno, 1973 is a proposed order of rays. It is a sister group to Rajiformes, the true rays, and contains the following families:* Dasyatidae * Gymnuridae * Mobulidae * Myliobatidae...
, containing the
eagle rayThe eagle rays are a group of cartilaginous fishes in the family Myliobatidae, consisting mostly of large species living in the open ocean rather than on the sea bottom....
s and their relatives; Rhinobatiformes, containing the
guitarfishThe guitarfish are a family, Rhinobatidae, of rays. The guitarfish are known for an elongated body with a flattened head and trunk and small ray like wings. The combined range of the various species is tropical, subtropical and temperate waters worldwide...
es (which may be further split into Rhynchobatiformes, containing the shovelnosed guitarfishes, and Rhiniformes, the sharkfin guitarfishes). The
MesozoicThe Mesozoic Era is one of three geologic eras of the Phanerozoic eon. The division of time into eras dates back to Giovanni Arduino, in the 18th century, although his original name for the era now called the "Mesozoic" was "Secondary" The Mesozoic Era is one of three geologic eras of the...
Sclerorhynchoidea are basal or
incertae sedisIncertae sedis , abbreviated "inc. sed.", is a term used to define a taxonomic group where its broader relationships are unknown or undefined.-Examples:The taxonomy for humans is usually recognized as follows:...
; they show features of the Rajiformes but have shouts resembling those of sawfishes.
Order Rajiformes (true rays)
- Family Anacanthobatidae (smooth skate
The smooth skates or leg skates are the ray family Anacanthobatidae. It contains a single genus Anacanthobatis, though in recent times the subgenus Sinobatis is occasionally elevated to full genus rank....
s)
- Family Dasyatidae (stingray
The stingrays are a family—Dasyatidae—of rays, cartilaginous fishes related to sharks. They are common in coastal tropical and subtropical marine waters throughout the world, but the family also includes species found in warmer temperate oceans such as Dasyatis thetidis, and species entirely...
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
The butterfly rays are a group of rays in the family Gymnuridae. They are found in warm oceans worldwide, and occasionally in estuaries....
s)
- Family Hexatrygonidae (sixgill stingray
The sixgill stingray, Hexatrygon bickelli, is an unusual species of deep-sea ray. It is distinguished by its long, soft snout and six pairs of gill slits . It is the sole member of the family Hexatrygonidae, in the order Rajiformes...
s)
- Family Myliobatidae (eagle ray
The eagle rays are a group of cartilaginous fishes in the family Myliobatidae, consisting mostly of large species living in the open ocean rather than on the sea bottom....
s). The largest of rays, including the giant manta rayThe manta ray , is the largest of the rays. The largest known specimen was more than across, with a weight of about . It ranges throughout tropical waters of the world, typically around coral reefs...
s. Most eagle rays have one poison-carrying spine.
- Family Plesiobatidae (deepwater stingray
The deepwater stingray or giant stingaree, Plesiobatis daviesi, is a species of ray and the only species in the family Plesiobatidae. The largest and most widespread of the stingarees, it is found on continental slopes from South Africa to Japan and Australia...
s)
- Family Potamotrygonidae
River stingrays are Neotropical freshwater fishes of the Potamotrygonidae family .They are native to northern, central and eastern South America, living in rivers that drain into the Caribbean, and into the Atlantic as far south as the Río de la Plata in Argentina...
(river stingrays)
- Family Rajidae (skate
Skates are cartilaginous fish belonging to the family Rajidae in the superorder Batoidea of rays. There are more than 200 described species in 27 genera.-Description and habitat:...
s)
- Family Rhinobatidae (guitarfish
The guitarfish are a family, Rhinobatidae, of rays. The guitarfish are known for an elongated body with a flattened head and trunk and small ray like wings. The combined range of the various species is tropical, subtropical and temperate waters worldwide...
es). They have a body structure similar that of the sawfishes, but are not thought to be closely related.
- Family Urolophidae (round ray
The round rays are a family, Urolophidae, of rays found in the Indo-Pacific.As their name implies, they have disc-shaped bodies, which are formed by wide pectoral fins that merge in front of the head. Most species have venomous spines on the tail, which is relatively long, and ends in a clear...
s)
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 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 imbedded animals. Sawfishes can enter freshwater rivers and lakes. Some species reach a total length of 6 metres (20 ft).
Order Torpediniformes (electric rays)
Electric rays have
organsIn biology and anatomy, an organ is a collection of tissues joined in structural unit to serve a common function ....
in their wings that generate
electric currentElectric current can mean, depending on the context, a flow of electric charge or the rate of flow of electric charge ....
. They are used to immobilize prey and for defense. The current is strong enough to stun humans, and the ancient Greeks and
RomanAncient Rome was a civilization that grew out of a small agricultural community founded on the Italian Peninsula as early as the 10th century BC. Located along the Mediterranean Sea, it became one of the largest empires in the ancient world....
s used these fish to treat ailments such as
headacheIn medicine a headache or cephalalgia is a symptom of a number of different conditions of the head. Some of the causes are benign while others are medical emergencies.There are a number of different classification systems for headaches...
s.
- Family Narcinidae
The numbfishes are a group of electric rays in the family Narcinidae. Some sources include the sleeper rays, family Narkidae, as a subfamily of the Narcinidae. They are bottom-dwelling cartilaginous fishes with large pectoral fin discs and long tails...
- Family Torpedinidae