Table of Contents Coral Reef Cart Collection

Vertebrates: Cartilaginous Fishes

Rays

Specimens

ray model

GENERAL INFORMATION

Classification

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  Phylum Chordata, Subphylum Vertebrata, Class Elasmobranchii
  
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  Rays belong to a group that also includes skates and sawfishes.
  

Distribution

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  Found in tropical and temperate seas around the world.
  

Habitat

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  Most species are marine, but many can penetrate estuarine waterways and even freshwater areas. One family of river stingrays is exclusively freshwater. Many rays live in shallow, coastal waters. Some, such as the pelagic stingray, live in open water.
  

Appearance and Behavior

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  Rays have skeletons made of cartilage. Their flattened bodies have large pectoral fins joined to their head and trunk with the tail trailing behind. When rays move, most swim by undulating their bodies like a wave; others flap their fins like wings.
  
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  Gills are on the underside of the ray. Clean water flows into the gill chamber through a circular opening just behind the eye, called a spiracle. (If water entered through the gills themselves, the gills might become clogged with sea bed mud.) Water exits through the gills. The five gill slits are visible on the underside of the ray.
  
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  The snout is sensitive as it noses in mud for food. The nostril is an opening to an olfactory organ and is guarded by a flap. Rays hunt mostly by scent.
  
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  The horny mouth on the underside is adapted for grasping shellfish, worms, fishes, and other bottom loving creatures. These creatures are ground up with flat jaw teeth.
  
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  Rays have large, movable eyes and good eyesight.
  
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  Many rays have a venomous spine (also known as a barb or stinger), but some do not. (The Academy’s bowmouth guitarfish is classified as a ray, but does not have a venomous sting.) In those that have the spine, it can be located in several positions. In the family Dasyiatidae (like the Academy’s honeycomb stingrays) the spine is relatively far back on the tail and can deliver a powerful blow. In the family Myliobatidae (like the Javanese cownose ray) the spine is at the base of the tail and is a less effective weapon.
  
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  The spine is actually a modified dermal denticle. (The ray’s skin is partially covered with dermal denticles—“skin teeth” that contain dentine like normal teeth.) The stinger can have serrated edges and a sharp point. Some rays have even two or three stingers. The stinger can be 5 to 16 inches long (12 – 40 cm). The rays’ venom glands are located in paired grooves on the underside of the spine. Rays use the venom mainly as a defense against larger predators. When threatened, a ray can lash its tail back and forth or arch it over its head, slashing and stabbing its stinger into the enemy. A stingray has even been seen making a threat display with the tail raised when a shark came too close. If a ray loses its tail spine, it immediately begins to grow a new one. Stingrays shed and re-grow their spines on a regular basis regardless of whether they use them.
  
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  The stingray has electrical sensors called “ampullae of Lorenzini.” Located around the stingray’s mouth, these organs sense the natural electrical charges of potential prey.
  
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  Rays often hide in the sand with only their eyes slightly exposed. The back of a ray may be camouflaged, while the underside need not be.
  
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  To uncover buried prey, rays force jet streams of water through their mouths or use the undersurface of their wing like a giant suction cup to suck buried prey out of their burrows.
  
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  Some rays visit “cleaning stations” where fish such as bluehead wrasses and Spanish hogfish eat parasites and mucus from the stingrays’ bodies.
  

Diet

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  Worms, fishes, shellfish
  

Predators

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  Sharks, whales, and larger rays
  

Reproduction and Development

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  Rays give birth to live young.
  

Conservation status

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  Some rays are fished for food, but are still in ample supply while others are at risk. Habitat degradation can also be a problem.
  

Remarks

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  Feeding stingrays is a tourist activity in some resorts. However, in rare cases the stings of some rays can be fatal to humans. Other effects include numbness, paralysis, difficulty breathing, and blood poisoning. If going swimming where there are rays, humans should shuffle their feet.
  
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  Stingray skin is processed into leather that’s strong and durable. At one time craftsmen used this rough leather for sandpaper and samurai warriors wore stingray leather armor. Modern tanning methods have made the leather more pliable so it is in demand for wallets and accessories.
  
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  The manta ray is the largest living ray with a wingspan exceeding 20 feet. It has lobed “scoops” (adapted from the front parts of the pectoral fins) on the front of the head to channel food into the great mouth. Despite their size, mantas have small teeth and are gentle filter feeders, cruising the upper waters of warm oceans and consuming plankton, small fishes, and shellfish. They can also leap up to 5 feet (1.5 m) from the water. Their name comes from the Spanish word for blanket.
  
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  There are also electric rays. An example is the Atlantic torpedo ray that lies on the sea floor for much of the time, but when it wants to feed on small fish and shellfish, it swoops in, wraps its pectoral fins around the victim and delivers shocks of over 200 volts from specialized muscle blocks on either side of its head.
  

To Notice

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  Notice the size and shape of the barb.
  
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  Note the position of the barb on a model or photo.
  
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  Notice the various ray body parts on a model or photo: gills, mouth, spiracles, eyes, nose.
  
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  Compare the anatomy, diet, and other characteristics of the manta ray to the blue-spotted stingray or other rays.
  

specimen (model) detail

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  Distribution: Throughout the tropical Indo-west Pacific from the Red Sea to the Philippines, Japan, and south to Australia
  
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  Habitat: Sandy bottoms near coral and rocky reefs, from intertidal zone to 50 m. It moves onto reef flats and into shallow lagoon waters at high tide.
  
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  Appearance: Dorsal color is reddish-brown to olive drab with blue spots and smaller black spots; ventral side is white. Tail with black and white bands is about as long as the body and usually has one stinging spine. Disc up to 50 cm wide.
  
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  Diet: Crabs and shrimp, also small fishes
  
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  Reproduction and Development: Ovoviviparous (eggs retained in the female’s body); embryos receive nourishment from a yolk sac.
  
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  Mortality/Longevity: Killer whales are known predators; probably also taken by other marine mammals and sharks.
  
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  Remarks: The tail can deliver a painful wound, but it usually only stings when it is inadvertently stepped on in turbid waters. It is caught commercially, but its small size makes it of limited value.
  

Manta Ray Manta birostris

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  Distribution: Tropical waters worldwide; sometimes in warm temperate areas.
  
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  Habitat: Manta rays usually swim at the surface in contrast to other rays that are bottom dwellers. They tend to congregate over high points on coral reefs where currents bring up plankton. Found at a depths of 0-24 m.
  
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  Appearance and behavior: The manta ray is the largest ray. Wingspan is up to 8 m and weight up to 1.8 metric tons (4000 lb).
  
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  When feeding, it swims along with its cavernous mouth wide open, beating its huge triangular wings slowly up and down. On either side of the mouth, which is at the front of the head instead of on the underside as in other rays, are two long lobes, called cephalic horns, which funnel plankton into the mouth. These are the origin of the manta’s other name—devil ray.
  
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  Diet: Plankton and small fish
  
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  Reproduction: Ovoviviparous. Despite their size, manta rays can leap from the water, occasionally giving birth to their young as they do so.
  
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  Remarks: Mantas may be sociable with divers in some sites and have been known to “dance” with them.
  

Sharks

Specimens

hammerhead and whale shark models

GENERAL INFORMATION

Classification

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  Phylum Chordata, Subphylum Vertebrata, Class Elasmobranchii
  

Distribution

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  Sharks are found in all the world's oceans.
  

Habitat

Appearance and Behavior

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  The streamlined, torpedo-like form of most sharks contributes to their success as efficient predators of the world's oceans. Shark skeletons are composed of cartilage rather than bone. Lacking a swim bladder, sharks increase buoyancy by means of a large, fatty liver; however, unless a shark swims actively, it will sink to the bottom.
  
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  Sharks vary in size from the whale shark, which may reach 50 feet, to species considerably less than a foot in length.
  
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  A shark may have from 6 to 20 rows of teeth, depending on the species. Usually only the first two rows of teeth are used for feeding. The others are replacement teeth that move forward in conveyor-belt fashion when older teeth are broken off. They may replace teeth every few days, thus keeping the functional rows razor sharp.
  
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  The teeth vary with the species; variations of size and shape are related to diet.
  
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  Shark teeth are modified scales, with the same basic structure as the denticles that cover the shark's skin and give it a sandpaper texture.
  

Diet

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  Most sharks are carnivorous, though the largest species—the whale shark and the basking shark—feed chiefly on plankton. Most sharks feed on each other or bony fish. A few seem to eat almost anything. A tiger shark was found to have shoes, a license plate, deer antlers, a chicken coop, and even medieval armor inside its body.
  

Predators

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  Adult sharks have few predators except each other, other large bony fishes, sea lions, and man.
  

Reproduction

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  The young of many sharks hatch from eggs and are born alive. Other sharks lay distinctive egg cases. Fertilization is internal.
  

Conservation Status

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  Overfishing has depleted shark populations around the world. As other fish stocks have been depleted, shark meat has gained in popularity in many countries, including the U.S. To satisfy the demand for shark fin soup, prized in Asian countries, fishing crews often catch a shark, cut off its fins, and throw the animal back.
  

Remarks

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  Most shark species pose little threat to man, either because they are unaggressive or relatively small. However, great white, tiger, bull, oceanic white tip, and hammerhead sharks have been known to attack humans. In the case of the great white, researchers suggest that many attacks on humans are caused by mistaken identity. The shark mistakes its victim for large sea mammals, such as sea lions or seals. Statistics show about 50 shark attacks occur a year, resulting in about five human deaths. CAS scientist John McCosker is a leading contributor to the understanding of sharks.
  

To Notice

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  Explain that the jaw is made from cartilage, not bone. The jaw is only loosely attached to the skull. When a shark bites its prey, the jaws move forward allowing the teeth to be used more efficiently.
  
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  Point out that the rows of teeth will move forward as replacements are needed.
  
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  Discuss how the diet, hunting strategies, and other behaviors of the hammerhead (model) and whale shark (model) might differ from the sandbar shark.
  

SPECIMEN details

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  Distribution: Globally distributed in temperate and tropical waters
  
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  Habitat: Bottom-dwelling, shallow coastal water species that prefers smooth substrate and avoids coral reefs.
  
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  Appearance: Averages 2 m (6.5 feet) in length. Has a taller than average dorsal fin; is bluish to brownish gray color.
  
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  Diet: It is a bottom feeder that eats small fishes, mollusks, and crustaceans.
  
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  Predators: Juveniles are preyed upon by larger sharks. Adults have few predators, except humans. It is the most common shark species caught in the U.S.
  
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  Reproduction: A female sandbar shark can become gravid every other year. Litter size varies by region. There can be 6-13 pups.
  
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  Conservation: It is listed as Near Threatened by the IUCN.
  

Whale Shark Model Rhincodon tipus

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  Distribution: Tropical and temperate waters worldwide.
  
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  Habitat: Most often seen in open seas, but comes near coral reefs, also. It is found near the surface but in deep water in winter.
  
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  Appearance and Behavior: The largest of all fish, the whale shark can grow up to 18 m long and weigh up to 12 metric tons. The pattern of white spots on the whale shark’s back is unique, enabling scientists to identify individuals.
  

These whales are placid and allow divers to hang onto their fins.

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  Diet: Plankton and small fish. To obtain the huge amount of food it needs, it sucks water into its mouth and pumps it over its gills where particles become trapped by bony projections called gill rakers. Water then passes over the gills where gas exchange occurs.
  

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  Reproduction: Whale shark eggs hatch inside the mother, and she gives birth to live young. The eggs are 40 times larger than chicken eggs.
  
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  Mortality/Longevity: Some scientists think they may live over 100 years.
  
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  Conservation Status: They are killed for their meat and fins although they are legally protected in some countries.
  
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  Remarks: Every year around April, whale sharks migrate to Ningaloo Reef off northwestern Australia for a plankton feast. The plankton explosion results from a simultaneous mass spawning of the reef’s corals, possibly triggered by a full moon.
  

Hammerhead Shark Model Sphyrna sp.

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  Distribution: Tropical and warm temperate waters worldwide.
  
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  Habitat: Can be found in deeper water, but also go up to shallow areas. They are found at depths of 0-500 m.
  
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  Appearance and Behavior: The largest hammerheads are more than 6 m in length. All have a flattened, T-shaped head. The eyes are at the ends of its head so as it swims it turns its head from side to side. The nostrils are near the ends of the head. Its sense of smell is thought to be ten times better than that of other sharks. They also find prey by detecting electrical signals that the prey sends out as it moves.
  

The shape of its head may act like a wing, giving the shark lift as it swims.

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  Diet: Fish, other sharks, octopuses, crustaceans, and stingrays. Hammerheads are not deterred by the ray’s venomous spines. Some have been found with 50 spines in their mouth and throat.
  
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  Reproduction: They give birth to live young in shallow bays and estuaries where the skin of the young darkens to give protection against sunlight.
  
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  Conservation Status: Almost all the hammerheads are at risk. The fins are among the most expensive shark fins when sold.