Batoidea is a superorder of cartilaginous fish commonly known as rays. They and their close relatives, the sharks, 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 fins that are fused to the head, and gill slits that are placed on their ventral surfaces.
Anatomy
Batoids are flat-bodied, and, like sharks, are cartilaginous marine fish, meaning they have a boneless skeleton 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 guitarfishes 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 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 fishes do, and passing it outward through the gills.
Reproduction
Batoids reproduce in a number of ways. As is characteristic of elasmobranchs, batoids undergo internal fertilisation. Internal fertilisation 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 (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 purses and which often wash up empty on beaches in areas where skates are common.
Habitat
Most species live on the sea floor, in a variety of geographical regions â€" mainly in coastal waters, although some live in deep waters to at least 3,000 metres (9,800 ft). Most batoids have a cosmopolitan distribution, preferring tropical and subtropical marine environments, although there are temperate and cold-water species. Only a few species, like manta rays, 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, oysters, crustaceans, and some fish, depending on the species. Manta rays feed on plankton.
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 recognizes four orders. The Mesozoic Sclerorhynchoidea are basal or incertae sedis; they show features of the Rajiformes but have snouts resembling those of sawfishes. However, evidence indicates they are probably the sister group to sawfishes
Order Torpediniformes
- Family Hypnidae (coffin rays)
- Family Narcinidae (numbfishes)
- Family Narkidae (sleeper rays)
- Family Torpedinidae (torpedo rays)
Order Rhinopristiformes
- Family Glaucostegidae (giant guitarfishes)
- Family Platyrhinidae* (fanrays)
- Family Pristidae (sawfishes)
- Family Rhinidae (wedgefishes)
- Family Rhinobatidae (guitarfishes)
- Family Trygonorrhinidae (banjo rays)
- Family Zanobatidae* (panrays)
* the placement of these families is uncertain
Order Rajiformes
- Family Anacanthobatidae (legskates)
- Family Arhynchobatidae (softnose skates)
- Family Gurgesiellidae (pygmy skates)
- Family Rajidae (skates)
Order Myliobatiformes
- Family Aetobatidae (pelagic eagle rays)
- Family Dasyatidae (whiptail stingrays)
- Family Gymnuridae (butterfly rays)
- Family Hexatrygonidae (sixgill stingrays)
- Family Myliobatidae (devilrays)
- Family Plesiobatidae (giant stingarees)
- Family Potamotrygonidae (Neotropical stingrays)
- Family Rhinopteridae (cownose rays)
- Family Urolophidae (stingarees)
- Family Urotrygonidae (round stingrays)
Difference between sharks and rays
Sharks and rays are both cartilaginous fishes which can be contrasted with bony fishes. Rays are adapted for feeding on the bottom. Guitarfish are somewhat between sharks and rays, and show characteristics of both (though they are classified as rays).
See also
- List of threatened rays
References
Notes
Bibliography
- Shark references . Database of bibliography of living/fossil sharks and rays (Chondrichtyes: Selachii) with more than 15.000 listed papers and many download links.
- Martin, R Aidan (February 2010), "Batoids: Sawfishes, Guitarfishes, Electric Rays, Skates, and Sting Rays", Elasmo research, ReefQuest Centre for Shark Research .
- McEachran, JD; Dunn, KA; Miyake, T (1996), "Interrelationships of the batoid fishes (Chondrichthyes: Batoidea)", Interrelationships of Fishes, Academic Press .
- McEachran, JD; Aschliman, N (2004), "Phylogeny of batoidea", in Carrier, JC; Musick, JA; Heithaus, MR, Biology of sharks and their relatives, Boca Raton: CRC Press, pp. 79â€"114 .
- Nelson, Joseph S (2006) Fishes of the World Edition 4, illustrated. John Wiley & Sons. ISBNÂ 9780471756446. PDF
External links
- "Rays Fact Sheet", Fisheries (PDF), Western Australia, archived from the original (PDF) on 2013-05-13Â .