 |
| Image shown at 100% of actual size |
|
SUNDAY, JULY 15, 2007
Man-O-War.
Find out the facts to this hazardous creature.
NCWATERMAN.COM - The Portuguese Man of War traps its food in its tentacles. It feeds mainly on fish fry (young fish) and herring, and it also consumes shrimp, other crustaceans, and other small animals in the plankton. Nearly 70 to 90% of the prey is fish, making the Man of War is a dominant invertebrate predator of fish larvae.
The tentacles, or dactylozooids, are the Man of War's main mechanisms for catching its prey. They are used for defense. The Man of War sometimes traps and consumes larger fishes such as flying fish and mackerel, though fishes as large as these generally manage to escape from the tentacles. The food of the Man of War is digested in its bag-lke stomachs (gasterozooid or siphon), which are located along the underside of the float. The gasterozooids digest the prey by secreting enzymes that break down proteins, carbohydrates and fats. Each Man of War has multiple gastersozooids complete with individual mouths. After the food has been digested, any undigestible remains are pushed out through the mouths. The nourishment from the digested food is absorbed into the body and eventually circulates to the different polyps in the colony.
Reproduction
An "individual" is actually a colony of unisexual organisms. Every individual has specific gonozooids (sex organs or reproductive parts of the animals, either male or female). Each gonozooid is comprised of gonophores, which are little more than sacs containing either ovaries or testes. Physalia are dioecious. Their larvae probably develop very rapidly to small floating forms. Fertilization of Physalia is assumed to occur in the open water, because gametes from the gonozooids are shed into the water. This may happen as gonozooids themselves are broken off and released from the colony. The release of gonozooids may be a chemical response occurring when groups of Physalia are present in one locality. Critical density is probably required for succesful fertilization. Fertilization may take place close to the surface. Most reproduction takes place in the fall, producing the great abundance of young seen during the winter and spring. It is not known what triggers this spawning cycle but it probably begins in the Atlantic Ocean.
Germ Cell Development
Each gonophore has a central spadix of multinucleate endodermal cells separating the coelenteron from a layer of germ cells. Covering each germ cell is a layer of ectodermal tissue. When gonophores first bud, the germ layer is a cap of cells on top of the endodermal spadix. As gonophores mature, the germ cells evolve into a thich layer covering the spadix. Spermatogonia form a thick layer, while oogonia form a convoluted band several cells wide, but only one cell layer thick. There is very little cytoplasm material within these cells, except during rare instances when cell division is encountered. Oogonia begin development at approximately the same size as spermatogonia, but expand considerably larger. All oogonia are apparently formed at an early stage of gonophore development prior to the occurrence of enlargement. Interestingly, there appears to be yolk globules within the cytoplasm of most oogonia.
Behavior
Locomotion is generally passive, driven by wind and current. The Portuguese Man of War is a floating hydrozoan colony. It is actually a colony consisting of four polyps: a pneumatophore, or float; dactylozooids, or tentacles; gasterozooids, or siphons; and, gonozooids. Nematocysts (stinging cells) are located in the tentacles. Their action is based on their individual osmotic and hydrostatic pressure. Sensory cells are numerous and are located in the epidermis of the tentacles and the region around the mouths. Generally, the sensory cells are receptors for touch and temperature.
The colony cannot swim and instead passively floats by the aid of its pneumatophore, or float. The Man of War's float is actually a long, gas-filled bladder, formed as an overgrown polyp in the shape of a closed bag. Some Men of War are "left-sided," while others are "right-sided." The "left-sided" individual drifts at an angle of 45 degrees to the right of the direction from which the wind is blowing, and the "right-sided" individual does the opposite. This distinction is crucial in the spreading of the animals more evenly over the warm oceans of the world.
An important aspect of the Man of War's behavior is the symbiotic relationship between the Man of War and each of the following: Nomeus (a minonwlike fish), the clownfish (commonly called the Man of War fish), and the yellow-jack. These fishes live within the tentacles of a Physalia and are rarely seen elsewhere. The fish, particularly the clownfish, produce a slimy mucus that causes the Man of War not to fire its nematocysts. When first introduced to a Man of War, a Nomeus initially swims near the surface and around the Physalia in a large circular pattern in both clockwise and counterclockwise directions. In addition, it avoid the larger dactylozooids and remain near the surface, feeding on the tentacles that lie just under the float. Instead of developing a "protective" mucus, the fish depends on its swimming abilities as its main mechanism of defense, while living in the venomous discharge of the Physalia.
Habitat
The Portuguese Man of War lives the surface of tropical, marine water. Generally, the colonies live in warm, tropical and subtropical water such as along the Florida Keys and coast, the Gulf Stream, the Gulf of Mexico, the Indian Ocean, the Caribbean Sea, and other warm areas of the Atlantic and Pacific oceans. It is especially common in the warm water of the Sargasso Sea.
Physalia hurts tourists and tourism in areas where it is common, due to stings (of neurotoxins) from its nematocysts. Much money is spent each year to treat swimmers who have been stung by the nematocysts of individuals that have washed up on beaches. The inflammatory response resulting from Physalia stings is due to the release of histamines from mast cells within the victim.
Physalia pile up and are abundant in the center of the waters of the Sargasso Sea due to the movements of the currents around it and the rotation of the Earth.
The Portuguese Man of War is the sole member of the class Siphonophore with a unisexual colony; it is distinguished by a contractile, horizontal float. Although Siphonophora are generally considered to be the most specialized hydrozoans, some researchers claim that it is in fact the most primitive order, with the medusa and the polyp not fully differentiated. Additional support for this view comes from the observation that the regenerative powers of the Man of War are poor, in contrast to most other jellyfish. An incredible aspect of Physalia is that it is indeed not a single animal, but a colony in which the individual organisms have come to share the tasks of survival.
The stinging cells, or nematocysts, are the characteristic food-getting mechanisms of jellyfish and their close relatives. Physalia have two sizes of nematocysts, some small and others are large. These nematocysts retain their potency long after the Physalia has been washed up along the shore, as many hikers along beaches have discovered to their dismay and discomfort.
|
LEAD NEWS STORY: