Page 175 - Biology_F5

Biology for Advanced Level Secondary Schools

phyla. The first eight phyla fall under the example miracidium larva in flukes, but
group of invertebrates (animals without lack cilia in adult stage.
a backbone), while the ninth phylum, (f) They are bilaterally symmetrical.
Chordata, includes some invertebrates
and vertebrates (animals having a (g) They have a very simple nervous
backbone). This book will deal with five system, with two nerve cords which run
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selected phyla, namely Platyhelminthes, down on either side of the body. They
Nematoda (Aschelminthes), Annelida, have two simple brains called ganglia,
Arthropoda, and Chordata. which are simple bundles of nerves.
(h) Some have two eyespots that help in
3.7.1 Phylum Platyhelminthes sensing the presence of light.

Task 3.12 (i) Some platyhelminths have hooks and
Use internet sources and the library suckers for attachment. Examples of
to search for information on phylum platyhelminths are tapeworms: Taenia
Platyhelminthes. solium, Taenia saginata, and flukes:
Fasciola hepatica and Fasciola
This is a group of flatworms. The worms gigantica. Most members of this
can be free living or parasites. One of the phylum are parasites while others such
best-known example of flatworms is the as Planaria are free living.
tapeworm.
Classification of Platyhelminthes
General Characteristics of phylum Phylum Platyhelminthes, has three
Platyhelminthes classes, namely class Cestoda, Trematoda
(a) They are dorso-ventrally flattened and and Turbellaria. Class Cestoda consists
some are unsegmented worms. Most of of endoparasite animals, such as the
them have mouth and gut with no anus. tapeworms, including Taenia solium
(b) They have flame cells in the mesoderm (pork tapeworm), Dipylidium caninum
for excretion and osmoregulation. (dog tapeworm) and Taenia saginata
(c) They are hermaphrodites with a (beef tapeworm). Class Trematoda
complex reproductive system, which comprises the flukes; example, Fasciola
prevents self-fertilisation, but favours hepatica and Fasciola gigantica (Liver
flukes) and the blood flukes Schistosoma
cross-fertilisation. haematobium and Schistosoma mansoni.
(d) They are triploblastic acoelomate Class Turbellaria consists of the free

animals, which have three body layers living worms such as Planaria. They are
(ectoderm, endoderm, and mesoderm) flatworms.
without a body cavity or coelom.

(e) Some have cilia on their outer surface Structure of a tapeworm
for locomotion, for example Planaria, An adult tapeworm (Taenia sp) consists of
others have cilia during larval stage, for a knob-like head or scolex, equipped with
hooks and suckers for attachment to the

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