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Let’s start learning more about Enterobius vermicularis, or pinworms of phylum Nematoda. Why do you think these worms are called pinworms in the first place? You guess it! It is due to the shape of their tail.

The male pinworms are approximately 2-5 mm while the female is larger at 8-13 mm. The defining characteristics of pinworms and what gives it its common name is shown on the female tail. The long, thin pointed tail distinguishes the female worm while the male pinworm has a curved, blunt posterior end with a single spicule.

Pictured above is a microscopic image of an adult female Enterobius vermicularis. The arrow shows how a long, pointed tail characterizes the female pinworms.

Pictured above are two microscopic images of an adult male E. vermicularis. The image on the left shows the posterior end of the tail. The image on the right is a close up of the male and the black arrow points to the esophageal bulb and the red arrow points to the curled posterior tail with a spicule. 

If you look at the photo above, paying close attention to the female pinworm, you can see that the vagina and the mouth are not near the tail, so the female worms do not use their tail for reproduction or feeding purposes. Also, pinworms move by wiggling back and forth in the human body without using its tail, and you can see that in the video below. So what is the function of the female tail? The functions of the female pinworm are not known, but the function of the tail of the male pinworms are known. The male tail is curved and blunt with a single spicule. The spicule can be used as a tool to open the vulva of female to transmit sperm, and the curved tail is a way for the male to clasp on to the female during reproduction.

The video shows how pinworms wiggle back and forth to move.

Pinworms also have a double bulb esophagus. The double bulb esophagus is muscular and uses for the expulsion of eggs, but other animals in phylum Nematoda, it is used to pump fluids and foods. The cephalic alae are located at the anterior end and while the function is not known it is related to the enhancement of the cuticle strength, the movement of the worm, and the fat storage.

Cephalic alae head of Enterobius vermicularis. 

Citations: 

https://msu.edu/course/zol/316/everscope.htm

http://parasite.org.au/para-site/text/enterobius-text.html

https://en.wikipedia.org/wiki/Alae_(nematode_anatomy)

http://www5.zzu.edu.cn/__local/8/67/31/31BC8ABA766FC4BBE2D5EE15E38_EE744CC5_47A00.ppt

Pinworms: Structure and Pathogenesis (With Diagram)