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11
Cestodes: Tapeworms

General Characteristics

Tapeworms can be classified into 2 orders—Pseudophyllidea and Cyclophyllidea.
The adult worm consists of 3 parts:

1. Head (Scolex)
It is the organ of attachment to the intestinal mucosa of the definitive host. In
parasites of the order Cyclophyllidea, the scolex possesses 4 suckers. In some
Cyclophyllidea like Taenia solium, scolex has an apical protrusion called rostel-
lum. The rostellum may or may not be armed with hooks. In parasites of the
order Pseudophyllidea, the scolex does not possess suckers but possesses a pair
of longitudinal grooves called bothria, by which it attaches to the intestine of the
host.
2. Neck
It is the part, immediately behind the head and is the region of growth from
where the new proglottids are being formed.
3. Proglottids (strobila)
The proglottids consist of immature followed by mature and gravid proglot-
tids. Tapeworms are hermaphrodites and every mature segment contains both
male and female reproductive organs. In the immature segments, the reproduc-
tive organs are not well developed. The gravid segments have uterus filled with
eggs. Tapeworms do not have a body cavity or alimentary canal. Nutrients are
absorbed via the cuticle. Rudimentary excretory and nervous systems are
present.
The eggs of Cyclophyllidea and Pseudophyllidea are different from each
other. In Cyclophyllidea, the embryo inside the egg is called the oncosphere
(hexacanth embryo). It is spherical and has 3 pairs of hooklets. In Pseudophyllidea,
the egg is operculated.

© Springer International Publishing AG 2017 117
R. Mahmud et al., Medical Parasitology,
https://doi.org/10.1007/978-3-319-68795-7_11