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CHAPTER 8 The Nematodes
Thick-walled
colorless shell
A
Flattened on one side
Developing larva
Size range: 48-60 m long by 20-35 m wide
B
48-60 m
C
D
FIGURE 8-2 A, Enterobius vermicularis egg. B, Enterobius vermicularis unembryonated egg, ×400. C, Enterobius vermicularis
immature embryonated egg, ×400. D, Enterobius vermicularis mature embryonated egg, ×400. (B-D courtesy
of WARD’S Natural Science Establishment, Rochester, NY.)
Enterobius vermicularis
(en”tir-o’bee-us/vur-mic-yoo-lair’is)
Common names: Pinworm, seatworm.
Common associated disease and condition
names: Enterobiasis, pinworm infection.
Morphology
Eggs. The typical Enterobius vermicularis
egg measures 48 to 60 µm in length by 20 to
35 µm in width (Fig. 8-2; Table 8-1). The somewhat
oval egg is characteristically flattened on
one side. The egg consists of a developing larva
surrounded by a conspicuous double-layered,
thick-walled colorless shell. The egg may be seen
at various stages of development, as shown in
Figure 8-2B (unfertilized egg referred to as being
unembryonated), Figure 8-2C (fertilized egg; also
known as an embryonated egg), and Figure 8-2D
(mature egg).
TABLE 8-1
Parameter
Enterobius vermicularis Egg:
Typical Characteristics at
a Glance
Description
Size 48-60 µm long, 20-35 µm
wide
Shape
Oval, one-side flattened
Embryo
Stage of development varies;
may be unembryonated,
embryonated, mature
Shell
Double-layered, thick, colorless
Adults. The adult female E. vermicularis
worm (Fig. 8-3) measures 7 to 14 mm in length
by up to 0.5 mm wide (Table 8-2). The yellowish-white
females are equipped with primitive
organ systems, including a digestive tract, intestinal
tract, and reproductive structures. In addition,
the adult female possesses a clear, pointed
tail that resembles a pinhead—hence, the