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Comparative studies of natural groups of organisms
prey (Figure 3.61).
Dorsal fin
Caudal fin
An eye Lateral line
Mouth
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Operculum
Pectoral fin Anal fin
Pelvic fin
Figure 3.61: Generalised structure of a tilapia their life cycle and physiology, many
amphibians are “tied” to water bodies in
Class Amphibia order to survive and reproduce. Normally,
This class includes amphibians such amphibians undergo metamorphosis from
as frogs, toads, caecilians as well as a juvenile, as an aquatic larval form into a
salamanders. Amphibians are tetrapod terrestrial adult.
with the exception of caecilians, which
are limbless. All amphibians lay eggs Distinctive features of class Amphibia
with the exception of some caecilians and Amphibians have the following distinctive
some toads. For example members of the features:
caecelian genera Scolecomorphus and (a) They dwell both in water and on land, as
Schistometopum give birth to young ones. they depend on water for reproduction,
Also the toad genus Nectophrynoides; hence the name amphibian, which
the members of this genus also give means double life.
birth to young ones. In the genus of
Nectophrvnoides there is the Kihansi (b) Amphibians’ offspring begin their life
Spray Toad (Nectophrynoides asperginis); cycle under water and breath by means
a small toad endemic to Tanzania with this of gills. As they grow to adulthood
unique characteristic of giving birth to they move to terrestrial and breathe by
live young toadlets. means of either skin or lungs.
(c) They have soft moist skin without
The word amphibia refers to “double life”, scale, used for gas exchange to
or life in water and on land. Amphibians supplement lungs and buccal cavity.
are cold-blooded (ectothermic)
vertebrates whose body temperature is not (d) Amphibian eggs have a jelly structure,
regulated by internal mechanisms. They which is prone to dehydration when
inhabit a wide range of habitats, ranging exposed to air.
from terrestrial to aquatic environments. (e) Amphibian’s fertilisation takes place
Most amphibians spend a part of their outside the female body (with the
life in aquatic environment and another exception of some caecilians and some
part in terrestrial environment. Due to toads, including the Kihansi spray toad
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