This article is no longer available online so an archived copy has been provided for your reference. - SWS
Source:
Web Site:
Mote Marine Laboratory http://www.mote.org/index.php?src=gendocs&ref=Stingrays
Accessed: March 19, 2014
Characterized by their flattened shape and long, spinebearing tails, stingrays are unique elasmobranchs and cartilaginous cousins of the sharks. Stingrays have pectoral fins that are fused to the sides of their rostrum or
“head.” External gill openings are located on the stingray’s ventral side or “underside.” There are about
200 species of stingrays in the scientific order
Myliobatiformes, which includes the giant stingarees (Family Plesiobatidae), sixgill stingrays (Family
Hexatrygonidae), stingarees (Family Urolophidae), river stingrays (Family Potamotrygonidae), whiptail stingrays (Family Dasyatidae), butterfly rays (Family Gymnuridae), eagle rays (Family
Myliobatidae), cownose rays (Family Rhinopteridae), and devil rays (Family Mobulidae).
Stingrays come in two different general “types” – the “benthic” (or bottom) stingrays and the “pelagic”
(or swimming) stingrays.
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Benthic ray, such as the Atlantic stingray pictured above, are often found buried in the sand. They usually have a rounded or “diamond-shaped” body and their stings, when present, are located near the middle or lower third of their “tail.” As mostly bottom feeders, these rays generally feed on worms, clams, shrimp, crabs, snails and occasionally fish.
Pelagic rays, like the spotted eagle ray (left) and the manta ray (right) above, are more active swimmers that have a “bat-like” shape. Pelagic stingrays have stings that are located close to the body, just behind their pelvic fins. Like bottom rays, most pelagic rays also fed largely on bottomdwelling organisms. However, the devil rays are mainly plankton feeders and use paddle-like cephalic or “head” lobes to direct plankton-rich water into their mouths.
Stingrays can be found in both freshwater and marine habitats throughout the world. Most of the river stingrays of the Family Potamotrygonidae live permanently in freshwater and have lost the ability to survive in marine habitats. Atlantic st ingrays living in Florida’s St. Johns River also seem to spend their entire life in freshwater, but are capable of adapting to saltwater in controlled laboratory settings. Other stingrays live mostly in saltwater. However, many species are “euryhaline” or capable of living in waters of a wide range of salinity. Therefore, these species can often be found in freshwater habitats for extended periods of time.
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The venom apparatus or “sting” of a stingray is a spine or modified dermal denticle (the scales covering sharks and stingrays) with two ventral grooves filled with venom-producing tissue. The venom apparatus is surrounded by a cell-rich covering or sheath that also may produce lesser amounts of venom. The venom itself is a largely protein-based toxin that causes great pain in mammals and may also alter heart rate and respiration. However, since it is proteinaceous, it can be inactivated by exposure to high temperatures. Because of this, immersion of the wound in hot water or application of a heat compress are recommended as an immediate treatment for unfortunate victims of a stingray injury or “envenomation.” Although this may reduce the initial pain of a stingray injury, victims should obtain medical assistance so that the wound can be properly examined and cleaned to avoid secondary infections or other complications.
As mentioned above, the sting on most pelagic stingrays is situated near the base of the tail. This may discourage predators from biting the animal near its vital organs. In contrast, the sting of most bottom-dwelling stingrays is located further away from the body, making it a more effective and dangerous “striking” weapon. However, it should be pointed out that the sting is purely a defensive weapon only and that the “striking” action is an involuntary response rather than a conscious
“attack.”
No! Some stingrays species do not possess stings, such as some of the butterfly rays and devil rays. There are also other “ray” species that do not belong to the Order Myliobatiformes, such as the guitarfishes (Order Rhinobatiformes, pictured below on the left), sawfishes (Order Pristiformes), electric rays (Order Torpediniformes, pictured below on the right) and the ray-like skates (Order
Rajiformes).
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As mentioned above, skates are a type of “ray” that differ considerably from stingrays of the Order
Myliobatiformes. Skates, such as the clearnose skate pictured on the left, do not possess venomous barbs like stingray s although many do have sharp thorns located on their dorsal surface and tails. Also, unlike stingrays, skates primarily live in marine habitats and rarely enter brackish or freshwater environments. The most prominent difference between the two groups is that all stingrays give birth to live young while skates reproduce by laying eggs in leathery capsules sometimes called mermaid ’s purses.
Believe it or not, yes! People frequently mistake the two pectoral fins of the cownose rays for a pair of sharks. This mistake is an easy one to make if you are not careful. The two tips of the ray ’s pectoral fins often break the surface as it is swimming through the water. These fin tips are sometimes confused for the dorsal fins of two sharks.
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