Zoology

Anatomy of a Manta Ray



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Manta rays are classified as a type of fish.  They are found in tropical, subtropical, and temperate waters around the world.  Manta rays belong to the biological family known as Mobulidae. The genus “Manta” contains two species of manta rays:  the Reef Manta Ray and the Giant Oceanic Manta Ray.  The Giant Oceanic Manta Ray is the largest type of manta ray in the world.  Its average width is about 22 ft. Oceanic manta rays can weigh up to 5000 lb, which is greater than the weight of a mid-size automobile.  In the marine world, only whales and sharks are larger.

Manta rays can be found in both salty and fresh water.  They are often found near coral reefs, or in lagoons or near coastlines.  They prefer warmer water, and feed close to the surface.  Although the larger manta rays tend to be solitary creatures, they are often accompanied by shoals of pilot fish.  Smaller rays may form shoals of their own.

The mouth of the manta ray is located at the top of its head.  It feeds upon plankton and shrimp, but will sometimes eat small fish as well.  Manta rays have about 300 rows of very small teeth, about the size of the head of a pin, which are, strangely enough, not used for eating. The teeth are thought instead to play a role in courtship.  Manta rays are filter feeders, which means that they take in water that is then filtered through their gills, trapping the food along the gill plates so that only water passes back out.  The food then passes down to the stomach.  Adult manta rays may consume up to 60 lb of food daily, and spend hours each day feeding.  

The manta ray is usually a night feeder.  It will move along slowly in a straight line when feeding, allowing the maximum amount of food to be filtered through its gills.  Manta rays swim by flapping the large, triangular pectoral fins for which they are well known.    (The word, “Manta”, is derived from a Spanish word meaning “blanket” or “cloak”.)  The cephalic fins are forward extensions of the pectoral fins that are located anteriorly on each side of the head.  These fins help guide food into the ray’s mouth.  The eyes are located laterally, on each side of the head, at the base of the cephalic fins.  The gills are located ventrally, or on the ray’s belly.  The prey are caught on the manta ray’s gill rakers, which are flat plates of spongy tissue covering the spaces between the gill bars.

Manta rays have a body coating that is thicker than that of other types of rays. This coating has a protective mucus layer that shields the ray from various marine infections.  Manta rays vary a lot in color pattern, especially on the shoulders and underbelly.  They have a skeleton with a vertebral column, skull (chondocranium), a pelvic girdle and basal and radial cartilages near the base of the pectoral fins.   Since the manta ray evolved from the stingray, it has a tail similar to the stingray, but the tail has no stinger or spine within it.  Contrary to popular opinion, manta rays are not dangerous to humans, perhaps aside from hazards caused by their size.  It was not a manta ray that killed the famous “Crocodile Hunter”, Steve Irwin, Australian wildlife expert.  It was a stingray.

Manta rays have fairly sophisticated internal organs.  Along with devil rays, they have the largest brain relative to body size of any type of fish.  Their behavior is social and complex.  They can sometimes be seen to be breaching, or jumping out of the water.  There is evidence to suggest that this behavior enables the ray to communicate with others of its species.  They also have a circulatory, gastrointestinal and reproductive system, including a heart, esophagus, stomach, liver, gallbladder and reproductive organs. 

The male reproductive organ in the manta ray is a penis-like organ called the clasper.  The female mantas have a uterus.  During mating, sperm is transferred to the female manta from the male through a groove in the clasper.   Manta rays actually have a courtship, in which several males chase a female for a period of time.  When one of the males is finally successful, he grasps the tip of the female’s pectoral fin between his teeth and then presses his body against hers.  He then inserts a clasper into the female’s vent, or cloaca. Copulation lasts about 90 seconds, and then fertilized eggs develop inside the female for about 9 to 12 months.  The eggs are hatched inside the female, and she then bears live young.  Birth occurs in shallow water, where the young mantas may remain for several years before venturing further offshore. 

Manta rays are sometimes afflicted with various types of marine parasites, as well as bites from their predators, which are mainly sharks and killer whales.  For this reason, they sometimes visit “cleaning stations”, or areas where there are many small fish, such as butterfly fish or wrasse, that remove dead, infected or parasite-infested flesh from the ray by simply eating it off of them.  Since the cleaner fish also get a steady food supply from chewing on the manta rays, this relationship is symbiotic, or mutually beneficial.  This link contains a beautiful close-up shot of a manta ray’s mouth.  

In order to flush oxygen-rich water continually over their gills, manta rays must swim constantly.  It is not known whether or not they sleep, although it is possible that they may have dormant rest periods of reduced activity.  There are threats to the manta ray that have been created by humans, such as the demand for their gills in Chinese medicine.  Mantas can also become entangled in coastal fishing nets set up by the local fishermen.  In the Philippines, manta ray flesh is considered a delicacy, so the rays are caught and eaten.

However, in 2011, Manta Rays were listed as an endangered species by the Convention on the Conservation of Migratory Species of Wild Animals (CMS).  Therefore, they are strictly protected in international waters.  There is also an organization known as the Manta Trust, which was formed in 2011 to coordinate global research and conservation efforts for the Manta Ray.  Their goal is to protect the rays and their habitat through public education and research. 

In 2009, a bill was also signed into law in the state of Hawaii, protecting Manta Rays within state marine waters.  This law established criminal penalties and fines for killing or capturing Manta Rays within Hawaii’s state waters.

Because of the difficulties associated with observing manta rays in their natural environment, there is not a large body of research on them available at this time.  But people are intrigued by manta rays.  Like the whale and the dolphin, they are intelligent creatures.  When divers swim near them, they watch with great curiosity. Although the relationship between humans and manta rays is still in its infancy, it is probable that a very interesting future lies ahead.

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ARTICLE SOURCES AND CITATIONS
  • InfoBoxCallToAction ActionArrowhttp://www.elasmo-research.org/education/topics/lh_manta_faq.htm
  • InfoBoxCallToAction ActionArrowhttp://www.mantaray-world.com/manta-ray-feeding.html
  • InfoBoxCallToAction ActionArrowhttp://www.flmnh.ufl.edu/fish/gallery/descript/mantaray/mantaray.html
  • InfoBoxCallToAction ActionArrowhttp://marinemegafauna.org/mantarays/
  • InfoBoxCallToAction ActionArrowhttp://www.elasmo-research.org/education/topics/lh_manta_faq.htm
  • InfoBoxCallToAction ActionArrowhttp://www.youtube.com/watch?v=p1uySJSG27M
  • InfoBoxCallToAction ActionArrowhttp://www.maldivesdivetravel.com/maldives-blog/the-best-manta-ray-season-in-the-maldives-2011.html
  • InfoBoxCallToAction ActionArrowhttp://www.mantatrust.org/about-us/the-manta-mission/
  • InfoBoxCallToAction ActionArrowhttp://hawaiihouseblog.blogspot.com/2009/06/manta-ray-bill-becomes-law.html