Tapeworms

General Characteristics:                  

                                                                                       
multicellular                                                                
eukaryotic                                    
heterotrophic
motile
hermaphrodites
    

    Tapeworms are members of the Phylum Platyhelminthes and the Class Cestoda.  Some other examples of organisms in the same phylum are planarian and flukes.  The common name for tapeworms is flatworms.

    Tapeworms are heterotrophic.  This means they live on other living things in which they depend on for food.  They cannot feed, digest and eliminate undigested particles of food simultaneously.  Muscular contractions in the upper end of the gut of tapeworms cause a strong sucking force by which the tapeworms ingest their food into small bits.  The gut is branched and extends throughout the body, functioning in both digestion and transport of food.  The cells that line the gut engulf most of the food particles by phagocyctosis.  Tapeworms lack digestive systems; they absorb food directly through their body walls.  They attach themselves to the intestine wall where they are bathed by dissolved nutrients. 

    Tapeworms are sessile, which means they cannot move on their own.

    Tapeworms have a tough outer covering that protects against the host's digestive juices.

    The tapeworms have long, flat bodies that are divided into three sections:  the scolex, the neck and the proglottid.  The scolex contains several suckers and may have hooks.  Each proglottid contains a complete set of male and female reproductive organs that produce sex cells.  Proglottids are formed in the section at the base of the neck, with the maturing ones moving farther back as new ones are formed in front of them.  The proglottids near the end of the body form mature eggs.  As these eggs are fertilized, the zygotes in the very last segment begin to differentiate and these segments become filled with embryos.  These embryos, each surrounded by a shell, emerge from the proglottid.  They emerge through either a pore or the ruptured body wall.  The embryos  leave their host with the feces and are deposited in water, on leaves or in other places from which they may be picked up by another animal. 

    Tapeworms lack circulatory systems which transport oxygen and food molecules in higher organisms.  

    The tapeworm excretes its waste directly from the gut but also by means of a network of fine tubules that has ciliated flame cells on the side branches.  Their nervous system is simple.

    Some interesting facts:  

Eye spots enable the tapeworm to distinguish light from dark; the worms move away from strong light. 
They have a ribbon-like body that may be up to 9 m (30ft) in length.  
At least 125 million humans are infected with the tapeworm disease. 
When a single individual is divided into two or more parts, each part can regenerate an entire new tapeworm.
Tapeworms can infect all kinds of mammals.
To kill the tapeworm disease, you can use a treatment called quinacine hydrochloride (Atabrine) or niclosamide.

        Economic importance:  Food source, labor recreation.

    To view larger picture of tapeworm, click on an image below.

 hymen_scolex.jpg (6848 bytes)        aduo2.jpg (5946 bytes)       hymen_eggs.jpg (7241 bytes)

    For more information on the tapeworm, go to the World of Science Web site.

    Bibliography:

    Raven, Peter H.  and Johnson, George B.  1992.  Biology Third Edition.  Mosby Year-Book Inc:  St.  Louis, Missouri.

    The Canadian Encyclopedia Plus Copyright.  1996.  McClelland and Stewart Inc. (CD ROM), Parasites.