Page 176 - Biology_F5

Comparative studies of natural groups of organisms

intestinal wall of the host; a neck region; (c) It has a thin and flattened body, which
and a series of flat, rectangular body provides a large surface area for gas
segments (or proglottids) generated by the exchange and absorption of digested
neck (Figure 3.42). The length of chain of food.
proglottids may reach up to 15 ft or 20 ft (d) Its body is covered by a living
(4.6 m–6.1 m) long. Terminal proglottids epidermal layer called the tegument,
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break off, and are egested in the feaces which produces antienzymes to protect
of the host. Nevertheless, the new ones it from hosts’ digestive enzymes.
are constantly formed at the neck of the
worm. As long as the scolex and the neck (e) It has a large number of ploglottids,
are intact, the worm is alive and capable which ensures production of a large
of growing. Rudimentary nervous and number of eggs, hence high chance of
excretory systems run the length of the survival.
worm, through the proglottids. However, (f) It can respire anaerobically; therefore,
there is no digestive tract; the worm it is able to live under low oxygen
absorbs the host’s digested food through concentration, such as in the host’s gut.
its cuticle or outer covering. (g) It is well adapted to osmotic pressure

Rostellum changes in the host’s body.
Hook Mature proglottid (h) It has flame cells, which collect
excretory material from all parts of
Scolex
the body.
Suckers Structure of a liver fluke
Neck
Morphologically, an adult liver fluke,
such as Fasciola hepatica and Fasciola
Immature proglottid
gigantica, have a flattened leaf shaped

Figure 3.42: Structure of Taenia solium appearance (Figure 3.43). In the anterior
part, there is a triangular projection with
Adaptations of Taenia sp. to its mode of a mouth surrounded by oral suckers at its
life apex. Ventrally, at the base of the projection,
Taenia sp. exhibits various special there are ventral suckers; and between the
adaptations to its parasitic mode of life as
follows: two types of suckers, there is a genital pore.
(a) It has scolex (head) with hooks and Posteriorly, there is a minute excretory pore.
suckers for fixation and attachment on The body is enclosed in a tough cuticle,
the host’s gut wall. However, Taenia which is extended into backward directed
saginata lack hooks. spines. Their muscle fibres have small

(b) It lacks alimentary canal because it glands with minute ducts. The mouth runs
absorbs digested food materials from into the oesophagus, which branches into
its hosts. two blind parts.

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