Batomorphi is adivision ofcartilaginous fishes, commonly known asrays; this taxon is sometimes considered as thesuperorderBatoidea, but the 5th edition ofFishes of the World classifies it as the division Batomorphi.[2][3] Batomorphi, along with theshark division Selachii, both compose the subclassElasmobranchii. Rays are the most speciose of cartilaginous fishes groups, with well over 600 species in 26families. Rays are distinguished by their flattened bodies, enlargedpectoral fins that are fused to the head, andgill slits that are placed on theirventral surfaces.
Like sharks, Batomorphs are cartilaginous fish (Chondrichthyes), meaning they have a bonelessskeleton made of a tough, elasticcartilage. Most batomorphs aredorsoventrally flattened, with a mantle-like body, though theguitarfishes andsawfishes are somewhat less flattened, while most sharks have a spindle-shaped body. Many species of batomorph have developed theirpectoral fins into broad flat appendages often referred to as the wings. Theanal fin is absent. The eyes andspiracles are located on top of the head. Bottom-dwelling batomorphs breathe by taking water in through the spiracles, rather than through the mouth as most fish do, and passing it outward through thegills, whose openings orgill slits lie under the pectoral fins on the underside, whereas a shark's are on the sides of the head. Most batomorphs have fiveventral gill slits, but theHexatrygonidae have six.[4]
Batomorphs have a ventrally located mouth and can considerably protrude their upper jaw (palatoquadrate cartilage) away from thecranium to capture prey.[5] The jaws haveeuhyostylic type suspension, which relies completely on thehyomandibular cartilages for support.[6] Most batomorphs have developed heavy, rounded teeth for crushing the shells of bottom-dwelling species such assnails,clams,oysters,crustaceans, and somefish, depending on the species. Manta rays feed onplankton using densegill rakers to capture them.
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 3,000 metres (9,800 ft). Most batomorphs have acosmopolitan distribution, preferring tropical and subtropical marine environments, although there are temperate and cold-water species. Only a few species, likemanta rays, live in the open sea, and only a few live in freshwater, while some batomorphs can live in brackish bays and estuaries.
As is characteristic of elasmobranchs, batomorphs undergointernal fertilization. Internal fertilization is advantageous to batomorphs 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.[7] Allskates and some rays areoviparous (egg laying) while other rays areovoviviparous, meaning that they give birth to young which develop in a womb but without involvement of aplacenta.[8]
The eggs of oviparous skates are laid in leathery egg cases that are commonly known asmermaid's purses 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.[8] Capture-induced parturition is rarely considered infisheries management despite being shown to occur in at least 12% of live bearing sharks and rays (88 species to date).[8]
Batomorphs belong to the ancient lineage of cartilaginous fishes. Fossildenticles (tooth-like scales in the skin) resembling those of today'schondrichthyans date at least as far back as theOrdovician, with the oldest unambiguous fossils of cartilaginous fish dating from the middleDevonian. Aclade within this diverse family, theNeoselachii, emerged by theTriassic, with the best-understood neoselachian fossils dating from theJurassic. The oldest confirmed ray isAntiquaobatis, from thePliensbachian ofGermany.[9] Theclade is represented today bysharks,sawfish, rays andskates.[10]
Molecular evidence refutes the hypothesis that skates and rays are derived sharks.[11] Themonophyly of theskates, thestingrays, and theelectric rays has long been generally accepted. Along withRhinopristiformes, these comprise the four traditionally accepted major batomorph lineages, as in Nelson's 2006Fishes of the World. However, the exact phylogeny of the major batomorph lineages, internally and with respect to one another, has been subject to diverse treatments. The followingcladogram is based on a comprehensivemorphological assessment of batomorph phylogeny published in 2004:[12]
However, a 2011 study significantly reevaluated the phylogeny of batomorphs, usingnuclear andmitochondrial DNA from 37taxa, representing almost all recognized families and all of the traditional four major lineages. This is a far more numerous and diverse set of sample taxa than in any previous study, producing findings reflected in the cladogram below.[1]
This study strongly confirmed the traditionally accepted internal monophyly of skates, stingrays, and electric rays. It also recoveredpanrays assister to the stingrays, as older morphological analyses had suggested. However, it found the Rhinopristiformes, including thesawfishes and various "guitarfishes", to beparaphyletic, comprising two distinct clades. Referred to as "Guitarfishes 1" and "Guitarfishes 2", the former contains only theTrygonorrhinidae, while the latter contains the remainder of Rhinopristiformes (the familiesGlaucostegidae,Pristidae,Rhinidae, andRhinobatidae). In addition, while traditional phylogenies often find electric rays to be the basalmost batomorphs, followed by the Rhinopristiformes, this analysis finds apolytomy between skates, electric rays, andthornbacks at the base of Batomorphi, with weak support for skates being the actual most basal lineage, followed by a clade uniting the electric rays and thornbacks.
TheMesozoicSclerorhynchoidea were long considered to bebasal orincertae sedis; they show features of the Rajiformes but have snouts resembling those of sawfishes. Though considered to be the sister group to sawfishes for a time,[13] they are now considered true skates (Rajiformes).[14]
The following cladograms are derived from phylogenetic analyses taken from a 2022 study of batomorphmorphology by Villalobos-Segura and colleagues;[14]
According to a 2021 study inNature, 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 has increased the global extinction risk of these species to the point where three-quarters are now threatened with extinction.[19][20][21] This is notably the case in the Mediterranean Sea - most impacted by unregulated fishing - where a recent international survey of theMediterranean Science Commission concluded that only 38 species of rays and skates still subsisted.[22]
^Rajiformes includeskates,guitarfishes, andwedgefishes. They are distinguished by the presence of greatly enlargedpectoral fins, which reach as far forward as the sides of the head, with a generally flattened body. The undulatory pectoral fin motion diagnostic to this taxon is known as rajiform locomotion. The eyes and spiracles are located on the upper surface of the body, and the gill slits on the underside. They have flattened, crushing teeth, and are generally carnivorous. Most species give birth to live young, although some lay eggs inside a protective capsule ormermaid's purse.
^ The electric rays haveelectric organs in their pectoral fin discs that generateelectric current. They are used to immobilize prey and for defense. The current is strong enough to stun humans, and theancient Greeks andRomans used these fish to treat ailments such asheadaches.[16]
^ The sawfishes are shark-like in form, having tails used for swimming and smallerpectoral 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 embedded animals. Sawfishes can enter freshwater rivers and lakes. Some species reach a total length of 6 metres (20 ft). All species of sawfish are endangered or critically endangered.[17]
^Motta, P.J.; Wilga, C.D. (2001). "Advances in the study of feeding behaviors, mechanisms, and mechanics of sharks".Environmental Biology of Fishes.60 (1–3):131–56.doi:10.1023/A:1007649900712.S2CID28305317.
^Wilga, C.A.D. (2008). "Evolutionary divergence in the feeding mechanism of fishes".Acta Geologica Polonica.58:113–20.
^"Reproduction overall". Risk Section, Bedford Institute of Oceanography & Marine Fish Species.Canadian Shark Research Lab. Skates and rays of Atlantic Canada. Northwest Atlantic Fisheries Center. Archived fromthe original on 16 January 2015. Retrieved27 May 2012.
^Douady, C.J.; Dosay, M.; Shivji, M.S.; Stanhope, M.J. (2003). "Molecular phylogenetic evidence refuting the hypothesis of Batoidea (rays and skates) as derived sharks".Molecular Phylogenetics and Evolution.26 (2):215–221.doi:10.1016/S1055-7903(02)00333-0.PMID12565032.
^McEachran, J.D.; Aschliman, N. (2004). "Phylogeny of batoidea". In Carrier, J.C.; Musick, J.A.; Heithaus, M.R. (eds.).Biology of sharks and their relatives. Boca Raton, Florida: CRC Press. pp. 79–114.
^Pacoureau, Nathan; Rigby, Cassandra L.; Kyne, Peter M.; Sherley, Richard B.; Winker, Henning; Carlson, John K.; Fordham, Sonja V.; Barreto, Rodrigo; Fernando, Daniel; Francis, Malcolm P.; Jabado, Rima W.; Herman, Katelyn B.; Liu, Kwang-Ming; Marshall, Andrea D.; Pollom, Riley A.; Romanov, Evgeny V.; Simpfendorfer, Colin A.; Yin, Jamie S.; Kindsvater, Holly K.; Dulvy, Nicholas K. (2021). "Half a century of global decline in oceanic sharks and rays".Nature.589 (7843):567–571.Bibcode:2021Natur.589..567P.doi:10.1038/s41586-020-03173-9.hdl:10871/124531.PMID33505035.S2CID231723355.
McEachran, J.D.; Dunn, K.A.; Miyake, T. (1996). "Interrelationships of the batoid fishes (Chondrichthyes: Batoidea)".Interrelationships of Fishes. Academic Press.
"Shark references". – database of bibliography of living/fossil sharks and rays (see Chondrichtyes: Selachii) with more than 15 000 listed papers and many download links.
"Rays Fact Sheet".Rays fact sheet(PDF). Fisheries (Report). Recreational fishing. Perth, Australia: Government of Western Australia. Archived fromthe original(PDF) on 13 May 2013.
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