Batoidea is a

superorder Order ( la, ordo) is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and ...

of cartilaginous fishes, commonly known as rays. They and their close relatives, the

shark Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachi ...

s, 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 fin Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as se ...

s that are fused to the head, and

gill slit Gill slits are individual openings to gills, i.e., multiple gill arches, which lack a single outer cover. Such gills are characteristic of cartilaginous fish such as sharks and rays, as well as deep-branching vertebrates such as lampreys. In co ...

s that are placed on their

ventral Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

surfaces.

Anatomy

Batoids are flat-bodied, and, like sharks, are cartilaginous fish, meaning they have a boneless

skeleton A skeleton is the structural frame that supports the body of an animal. There are several types of skeletons, including the exoskeleton, which is the stable outer shell of an organism, the endoskeleton, which forms the support structure inside ...

made of a tough, elastic cartilage. Most batoids have five

slot-like body openings called gill slits that lead from the

gills A gill () is a respiratory organ that many aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow respiration on land provided they are ...

, but the

Hexatrygonidae The sixgill stingray (''Hexatrygon bickelli'') is a species of stingray and the only extant member of the family Hexatrygonidae. Although several species of sixgill stingrays have been described historically, they may represent variations in a ...

have six. Batoid gill slits lie under the

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 The guitarfish, also referred to as shovelnose rays, 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 tro ...

es 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 Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as see ...

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 fish do, and passing it outward through the gills.

Reproduction

Batoids reproduce in a number of ways. As is characteristic of elasmobranchs, batoids undergo

internal fertilization Internal fertilization is the union of an egg and sperm cell during sexual reproduction inside the female body. Internal fertilization, unlike its counterpart, external fertilization, brings more control to the female with reproduction. For inte ...

. 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 Oviparous animals are animals that lay their eggs, with little or no other embryonic development within the mother. This is the reproductive method of most fish, amphibians, most reptiles, and all pterosaurs, dinosaurs (including birds), and m ...

(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 purse An egg case or egg capsule, often colloquially called a mermaid's purse, is the casing that surrounds the eggs of oviparous sharks, skates and chimaeras. Egg cases typically contain one embryo, except for big skate and mottled skate egg case ...

s 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 and rays when fished. Capture-induced parturition is rarely considered in

fisheries management The goal of fisheries management is to produce sustainable biological, environmental and socioeconomic benefits from renewable aquatic resources. Wild fisheries are classified as renewable when the organisms of interest (e.g., fish, shellfish, ...

despite being shown to occur in at least 12% of live bearing sharks and rays (88 species to date).

Habitat

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 . Most batoids have a

cosmopolitan distribution In biogeography, cosmopolitan distribution is the term for the range of a taxon that extends across all or most of the world in appropriate habitats. Such a taxon, usually a species, is said to exhibit cosmopolitanism or cosmopolitism. The extr ...

, preferring tropical and subtropical marine environments, although there are temperate and cold-water species. Only a few species, like

manta ray Manta rays are large rays belonging to the genus ''Mobula'' (formerly its own genus ''Manta''). The larger species, '' M. birostris'', reaches in width, while the smaller, '' M. alfredi'', reaches . Both have triangular pectoral fins, horn-s ...

s, live in the open sea, and only a few live in freshwater, while some batoids can live in brackish bays and estuaries.

Feeding

Most batoids have developed heavy, rounded teeth for crushing the shells of bottom-dwelling species such as snails,

clams Clam is a common name for several kinds of bivalve molluscs. The word is often applied only to those that are edible and live as infauna, spending most of their lives halfway buried in the sand of the seafloor or riverbeds. Clams have two she ...

oysters Oyster is the common name for a number of different families of salt-water bivalve molluscs that live in marine or brackish habitats. In some species, the valves are highly calcified, and many are somewhat irregular in shape. Many, but not all ...

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapoda, decapods, ostracoda, seed shrimp, branchiopoda, branchiopods, argulidae, fish lice, krill, remipedes, isopoda, isopods, barnacles, copepods, ...

s, and some

fish Fish are Aquatic animal, aquatic, craniate, gill-bearing animals that lack Limb (anatomy), limbs with Digit (anatomy), digits. Included in this definition are the living hagfish, lampreys, and Chondrichthyes, cartilaginous and bony fish as we ...

, depending on the species. Manta rays feed on

plankton Plankton are the diverse collection of organisms found in water (or air) that are unable to propel themselves against a current (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they provide a cruc ...

Evolution

Batoids belong to the ancient lineage of cartilaginous fishes. Fossil denticles (tooth-like scales in the skin) resembling those of today's chondrichthyans date at least as far back as the

Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. T ...

, with the oldest unambiguous fossils of cartilaginous fish dating from the middle

Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, wh ...

. A

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English ter ...

within this diverse family, the Neoselachii, emerged by the

Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest per ...

, with the best-understood neoselachian fossils dating from the

Jurassic The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The Jurassic constitutes the middle period of ...

. The oldest confirmed ray is ''

Antiquaobatis ''Antiquaobatis'' is an extinct genus of ray from the Early Jurassic (Late Pliensbachian) of Europe, containing the single species ''A. grimmenensis''. It is the oldest known described member of the Rajiformes, and is based on a single tooth fro ...

'', from the

Pliensbachian The Pliensbachian is an age (geology), age of the geologic timescale and stage (stratigraphy), stage in the stratigraphic column. It is part of the Early Jurassic, Early or Lower Jurassic epoch (geology), Epoch or series (stratigraphy), Series an ...

Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwee ...

. The

is represented today by

s, sawfish, rays and

skate Skate or Skates may refer to: Fish * Skate (fish), several genera of fish belonging to the family Rajidae * Pygmy skates, several genera of fish belonging to the family Gurgesiellidae * Smooth skates or leg skates, several genera of fish belongi ...

Classification

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 ''Fishes of the World'' by the American ichthyologist Joseph S. Nelson (1937–2011) is a standard reference for fish systematics. Now in its fifth edition (2016), the work is a comprehensive overview of the diversity and classification of the ...

'' recognizes four orders. The

Mesozoic The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretace ...

Sclerorhynchoidea are basal or ''

incertae sedis ' () or ''problematica'' is a term used for a taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertain ...

''; they show features of the Rajiformes but have snouts resembling those of sawfishes. However, evidence indicates they are probably the sister group to sawfishes. Phylogenetic tree of Batoidea: Heliobatis radians Green River Formation (cropped)

Heliobatis radians Green River Formation (cropped)

Order Torpediniformes * Family Hypnidae (coffin rays) * Family

Narcinidae Narcinidae, or numbfishes, are a family of electric rays (order Torpediniformes). They are bottom-dwelling cartilaginous fishes with large, rounded pectoral fin discs and long tails. They can produce an electric discharge for defense, from which ...

(numbfishes) * Family

Narkidae Members of the family Narkidae are commonly known as sleeper rays. They are restricted to the temperate and tropical Indo-West Pacific from South Africa to Japan to Indonesia, and are exclusively marine and are absent from freshwater habitats. T ...

(sleeper rays) * Family Torpedinidae (torpedo rays) Order Rhinopristiformes * Family

Glaucostegidae ''Glaucostegus'', also known as giant guitarfishes, is a genus of large Indo-Pacific rays, with a single species, ''Glaucostegus cemiculus'', in the East Atlantic, and Mediterranean. They were formerly classified in the family Rhinobatidae but ar ...

(giant guitarfishes) * Family Platyrhinidae* (fanrays) * Family Pristidae (sawfishes) * Family

Rhinidae Wedgefishes are rays of the family Rhinidae, comprising eleven species in three genera. Classified in the order Rhinopristiformes along with guitarfishes and sawfishes, they have also been known as giant guitarfishes or sharkfin guitarfishes. ...

(wedgefishes) * Family Rhinobatidae (guitarfishes) * Family

Trygonorrhinidae Trygonorrhinidae, the banjo rays, is a family of rays, comprising eight species in three genera. They were formerly classified in the family Rhinobatidae. Taxonomy * ''Aptychotrema'' Norman, 1926 ** '' Aptychotrema rostrata'' Shaw, 1794 (Easte ...

(banjo rays) * Family Zanobatidae* (panrays) * the placement of these families is uncertain Order Rajiformes * Family

Anacanthobatidae The Anacanthobatidae, the smooth skates or leg skates, are a family of skates found at depths below in the Indian, Pacific and Atlantic Oceans. They lack the dorsal denticles (sharp, tooth-like scales) of other rays, hence their name, from G ...

(legskates) * Family

Arhynchobatidae Arhynchobatidae is a family of skates and is commonly known as the softnose skates. It belongs to the order Rajiformes in the superorder Batoidea Batoidea is a superorder of cartilaginous fishes, commonly known as rays. They and their close r ...

(softnose skates) * Family

Gurgesiellidae Pygmy skates are cartilaginous fish belonging to the family Gurgesiellidae in the superorder Batoidea Batoidea is a superorder of cartilaginous fishes, commonly known as rays. They and their close relatives, the sharks, comprise the subclass ...

(pygmy skates) * Family Rajidae (skates) Order Myliobatiformes * Family Aetobatidae (pelagic eagle rays) * Family Dasyatidae (whiptail stingrays) * Family Gymnuridae (butterfly rays) * Family

(sixgill stingrays) * Family Myliobatidae (devilrays) * Family

Plesiobatidae The deepwater stingray or giant stingaree (''Plesiobatis daviesi'') is a species of stingray and the sole member of the family Plesiobatidae. It is widely distributed in the Indo-Pacific, typically over fine sediments on the upper continenta ...

(giant stingarees) * Family Potamotrygonidae (Neotropical stingrays) * Family Rhinopteridae (cownose rays) * Family

Urolophidae The Urolophidae are a family of rays in the order Myliobatiformes, commonly known as stingarees or round stingrays. This family formerly included the genera '' Urobatis'' and '' Urotrygon'' of the Americas, which are presently recognized as form ...

(stingarees) * Family

Urotrygonidae Urotrygonidae is a family of rays in the order Myliobatiformes, commonly referred to as the American round stingrays or round rays. They are native to the tropical and warm temperate marine waters of the Americas. The two genera in this family ...

(round stingrays)

Conservation

According to a 2021 study in ''

Nature Nature, in the broadest sense, is the physical world or universe. "Nature" can refer to the phenomena of the physical world, and also to life in general. The study of nature is a large, if not the only, part of science. Although humans are ...

'', the number of oceanic sharks and rays has declined globally by 71% over the preceding 50 years, jeopardising "the health of entire ocean ecosystems as well as food security for some of the world's poorest countries".

Overfishing Overfishing is the removal of a species of fish (i.e. fishing) from a body of water at a rate greater than that the species can replenish its population naturally (i.e. the overexploitation of the fishery's existing fish stock), resulting in t ...

has increased the global extinction risk of these species to the point where three-quarters are now threatened with extinction. This is notably the case in the Mediterranean Sea - most impacted by unregulated fishing - where a recent international survey concluded that only 38 species of rays and skates still subsisted.Guide of Mediterranean Skates and Rays. Oct. 2022. Mendez L., Bacquet A. and F. Brian

/ref>

Differences between sharks and rays

All sharks and rays are cartilaginous fishes, Bony versus cartilaginous, contrasting with bony fishes. Many rays are adapted for feeding on the bottom.

Guitarfish The guitarfish, also referred to as shovelnose rays, 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 tro ...

es are somewhat between sharks and rays, displaying characteristics of both (though they are classified as rays).

Footnotes

References

Bibliography

* *

External links

* – database of bibliography of living/fossil sharks and rays (''see'' Chondrichtyes: Selachii) with more than 15 000 listed papers and many download links. * {{Authority control Extant Early Triassic first appearances Fish superorders