Morphology

Mirror mirror on the wall....

 

Taenia saginata has a very distinctive morphology.   This flatworm can grow in length from 4 to 12 meters long and 2 milimeters in diameter consisting of a scolex, neck, and strobila.  Adults possess a flat, ribbon-like body shape that is important for absorbing nutrients from its hosts’ intestine.  It does not have a digestive system: no mouth, no anus, or digestive tract.  It is also an acoelmate, meaning that it does not have a body cavity.  Taenia saginata is not a segmented worm but appears to be because of its strobila.

Taenia saginata strobila and the specific different segments called proglottids.

 Proglottids

The strobila consists of a chain of proglottids, which are basically gravid, or egg-filled segments.  Newer proglottids are produced at the neck and new growth will push the older more mature proglottids towards the posterior end where they will break off and release the thousands of eggs.  This is essential in the complicated life cycle of this tapeworm.   Taenia saginata is the largest of its genus consisting between 1000 to 2000 proglottids and can also have a lifespan of 25 years in a hosts’ intestine.  With this many proglottids it is not surprising that this parasite can grow up to an astounding 25 meters long!

A microscopic view of a gravid segment, proglottid in a pink stain that shows the uterus branching.

A gravid segmented proglottid stained with india ink, again showing the uterus branching.

 

 Check out this link to a video of a proglottid that was passed out of the intestine!

 

Scolex

 Taenia saginata has a distinct characteristic called the scolex.  The scolex is composed of four suckers at the anterior end of the flatworm that is used as a means to connect to the intestinal wall of its host. 

A close up view of the Taenia saginata's scolex comprised of four suckers and no hooks.

A close up view of the Taenia saginata's scolex with four suckers and no hooks.

 

 

 

 

 

 

 

 

 

 

 

Taenia saginata does not have any hooks on its scolex unlike its close relative the Taenia solium also known as the pork tapeworm that infects the common domesticated pig. You can see below a clear example of the hooks present in between the four suckers.

Taenia solium, the Pork tapeworm and its scolex with four suckers and hooks present in the center.

 A characteristic that both tapeworms of these do share is their almost identical eggs.  The larval form of T. saginata is in an egg that has a protective thick shell call the oncosphere. 

A microscopic view of the Taenia saginata's egg with a thick shell called the oncosphere.                A microscopic view of the Taenia saginata's egg with a thick shell called the oncosphere.

 

The next form is the larval cyst, and these occur in the intermediate host, the cow’s muscle fibers and it comprises of a single inverted scolex.  These cysts are also known as “Beef Measles.”    

Now check out the habitat and nutrition of this parasite! 

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