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Morphology of Gnathostoma



            Adult Gnathostoma are usually about 2 to 3 centimeters long and are rust-colored (Rusnak and Lucey 1993). With respect to morphological structure, third-stage larval worms have been studied more intensively than adults, as it is these larval worms that cause gnathostomiasis. Gnathostoma larvae usually have four rows of hooklets extruding from the surface of the cephalic bulb, which help in lodging into the tissues of their hosts. Tiny, cuticular spines run along the length of their bodies. Two types of papillae extend from the worm--a cervical papilla off the main body and two labial papillae on the cephalic bulb. Four sac-like openings in the cephalic bulb generate worm movement by expanding and contracting, and subsequently displacing nearby fluids (Ibid). 



Left: A microphotograph of G. spinigerum beneath a coverslip (Biswas et al. 1994). 

Right: A photograph of G. nipponicum (Taniguchi et al. 1991).


              Third-stage larval worms have been found ranging in size from approximately 2 millimeters to more than 16 millimeters (Ibid). The worms have both a "mouth" and an anus. At the tip of the cephalic bulb are two lips, through which nutrients are ingested. As with many parasites, there has been a process of streamlining and evolutionary simplification in these worms. The digestive tract of Gnathostoma is not complex and is comprised of just an esophagus and an intestine. 


Click on photo for enlargement.


            During reproduction, eggs are released from the vulval opening at the worm's posterior. The eggs of Gnathostoma are ovular with a mucus plug at one end (Ibid). They range in size from approximately 40 micrometers to 70 micrometers (Ibid). These eggs are released by adult worms into their hosts' digestive tracts, from which they will be excreted with the hosts' feces. 


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