Figure;2.17: Crab
Adaptation of Crab to its habitat
❖ Have exoskeleton for protection against enemies
❖ They have pincer like claw at edges for catching prey
❖ Possess gills for respiration
❖ Their legs are modified for swimming
4. Class Diplopoda
Class Diplopoda The class Diplopoda consists of members with many
legs; usually two pairs of legs per body segment. An example of a
member of class Diplopoda is a millipede. The head bears one pair of
antennae and a pair of mouthparts (jaws) while the trunk is not divided
into thorax and abdomen. They are scavengers that feed on decaying
organic matter, like leaves and compost. Distinctive features of class
Diplopoda
Diplopods have unique features, which differentiate them from other
Arthropods.
❖ They have two pairs of legs in each body segment
❖ Have cylindrical body (segmented)
❖ Have one pair of antennae
❖ They Curl up when disturbed or at rest
❖ Have two clusters of compound eyes example millipede.
❖ Mainly herbivores
❖ Gaseous exchange is by tracheal system.
❖ Mainly terrestrial
Millipede
Habitat: In cool dark places.
Economic importance of millipede.
❖ Used for biological studies
❖ Add soil fertility when die and decomposed
❖ Creates soil aeration i.e., pore spaces in the soil.
Adaptations of the millipede to its mode of life
Millipedes have the following features that make them adapt to their
environment:
❖ They have many, short and strong legs that enable them to burrow
into the soil.
❖ They produce special secretions, which help them to moisturize
dead organic matter on which they feed upon.
❖ A millipede tends to curl up into a tight flat coil for self-defense,
and protect their delicate legs inside an armoured exoskeleton.
❖ Millipedes produce an offensively odorous fluid (repugnatorial
fluid) when provoked, this acts as a defense against predators.
Figure;2.18: Millipede
Adaptation of millipede to its habitat
❖ They have many, short and strong legs that enable them to burrow
into the soil.
❖ They produce special secretions, which help them to moisturize
dead organic matter on which they feed upon.
❖ A millipede tends to curl up into a tight flat coil for self-defence,
and protect their delicate legs inside an armoured exoskeleton.
❖ Millipedes produce an offensively odorous fluid (repugnatorial
fluid) when provoked, this acts as a defence against predators.
5. Class Chilopoda
This class consists of organisms found in terrestrial environment. They
are terrestrial animals abundant in moist areas, such as leaf litters,
under logs or rocks. An example of chilopoda is centipedes.
The distinguishing characteristics of class chilopoda
❖ They have a flattened body with a distinct head. However, other
body segments are similar; the trunk is not obviously divided into
thorax and abdomen.
❖ They have one pair of legs per segment.
❖ They are carnivores, feeding mainly on insects and worms.
❖ Their first trunk segments have appendages, which are modified
into a pair of poisonous fangs.
Figure;2.19: Centipede
Habitat: In cool dark places, under logs/stones.
Adaptations of the centipede to its mode of life
Centipedes are adapted to a wide range of habitats because:
❖ They are fast moving animals; this helps them to catch their prey.
❖ They feed on insects, spiders, and worms, which they hunt and
paralyse with a bite of their poisonous claws.
❖ They have antennae for sensation.
❖ They have poisonous claws for defence and hunting.
❖ They have legs for locomotion.
❖ The last pair of legs has hooks for defence.
Economic importance Centipede.
❖ Used for biological studies
❖ Add soil fertility when decomposed
❖ Can sting and bite leading to poisoning
b. Phylum Platyhelminthes
This is a group of flatworms. The worms can be free living or parasites.
One of the best-known examples of flatworms is the tapeworm
General Characteristics of phylum Platyhelminthes
❖ They are dorsoventrally flattened and some are unsegmented
worms.
❖ Most of them have mouth and gut with no anus.
❖ They have flame cells in the mesoderm for excretion and
osmoregulation.
❖ They are hermaphrodites with a complex reproductive system,
which prevents self-fertilisation, but favours cross-fertilization.
❖ They are triploblastic acoelomate animals, which have three body
layers (ectoderm, endoderm, and mesoderm) without a body cavity
or coelom.
❖ Some have cilia on their outer surface for locomotion, for example
Planaria, others have cilia in larval stage, for example miracidium
larva in flukes, but lack cilia in adult stage.
❖ They exhibit bilateral symmetry.
❖ They have a very simple nervous system, with two nerve cords
which run down on either side of the body. They have two simple
brains called ganglia, which are simple bundles of nerves.
❖ Some have two eyespots that help in sensing the presence of light.
❖ Some platyhelminths have hooks and suckers for attachment.
Examples of platyhelminths are Taenia solium, Taenia saginata
(tapeworms), and Fasciola hepatica (liver fluke). Most members
of this phylum are parasites while others are free living, for
example: Planaria.
Classes of Phylum platyhelminthes
(a) Class Trematoda
(b) Class Cestoda
(a) Class Trematoda
Habitat: Found in the liver of animals like sheep, cattle, rabbit e.g. liver
flukes (fasciola hepatica). Found in the blood of animals e.g. Blood
flukes (Schistostoma).
Characteristics of Trematoda
❖ They are endoparasitic flat-worms
❖ Dorsal ventrally flattened
❖ They reproduce either sexually or asexually example liver fluke
❖ That cause ‘liver rot’ disease in sheep and cattle) blood fluke that
causes schistomiasis in man. The disease is also called bilharzias.
❖ They have leaf-like shape
Economic Importance
❖ Liver fluke cause liver rot disease
❖ Blood fluke cause disease called schistosomiasis (bilharzia)
Figure;2.20: Liver fluke
Adaptations of the liver fluke to its mode of life
❖ It has suckers that provide a means of attachment to the host.
❖ It has tegument with spines that prevent it from being washed
away by bile; and also help the parasite to erode liver cells.
❖ The tough tegument and secretions from the glands prevent the
worm from the effects of the host’s toxins.
❖ The parasite secretes enzymes that help it to penetrate the liver
cells at various stages of its life cycle.
❖ It has mechanisms and chemicals that suppress the actions of the
host’s digestive enzymes
b) Class Cestoda
It includes the group of tapeworms.
Habitat -found in the intestine of man, cattle, sheep.
Tapeworm-e.g.Taenia saginata found in the intestines of pigs.
Tapeworm -e.g.Taenia solium found in the intestine of catles
Characteristics of Class Cestoda.
❖ Dorso- ventral flattened
❖ Have smooth skin surface, for easy diffusion /absorption of
nutrients
❖ Some have hooks and suckers for attachment to their hosts.
❖ Reproduce asexually by fragmentation. Each fragment has
both male and female parts and produce fertilized eggs.
❖ They have thick cuticle for protection
Tapeworm
Habitat –small intestine of vertebrates.
Economic importance of Tapeworm
❖ Cause disease called taeniasis.
❖ Used for biological studies
Figure;2.21: Tapeworm
Adaptation of Tapeworm to its habitat
❖ It has scolex (head) with hooks and suckers for fixation and
attachment on the host’s gut wall
❖ It lacks alimentary canal because it absorbs digested food materials
from its hosts.
❖ It has a thin and flattened body, which provides a large surface
area for gaseous exchange and absorption of digested food.
❖ Its body is covered by a living epidermal layer called the tegument
which produces antienzymes to protect it from hosts’ digestive
enzymes.
❖ It has a large number of ploglottids, which ensures production of a
large number of eggs, hence high chance of survival.
❖ It can respire anaerobically; therefore, it is able to live under low
oxygen concentration, for example in the host’s gut
❖ It has flame cells, which collect excretory material from all parts of
the body.
Phylum Aschelminthes (Nematoda)
It includes the group of roundworms
The word ‘aschelminthes’ originates from two Greek words. ‘Aschel;
means round and ‘Minthos’ means worm.
Characteristic features of Aschelminthes
❖ Have round or cylindrical body
❖ Have pointed body ends
❖ Have un-segmented body
❖ Are parasite of vertebrates but some are free-living
❖ Have mouth and anus
❖ Body covered with thick elastic cuticle
❖ They have separate sex
❖ Examples of nematodes – Ascaris.
❖ Bilateral symmetry
❖ They are triploblastic
Ascaris
Habitat:small intestine of man, poultry guinea pig, pigs
Adaptations of Ascaris to its mode of life
❖ It has a tough cuticle, which protects it from being digested by the
enzymes of the alimentary canal of the host.
❖ It produces chemicals, which act as anti-enzymes to the digestive
enzymes of the host.
❖ It has an alimentary canal, which opens at the mouth and anus.
This enables the parasite to take food from the hosts’ digestive
system.
❖ It possesses digestive enzymes in its digestive system for the
completion of partially digested food from the hosts’ alimentary
canal.
❖ It has sensory papillae around its mouth for detecting food present
in the elementary canal of the host.
❖ It respires anaerobically, and have low metabolic rate; hence, they
are able to live inside the host’s intestine.
❖ It has high reproductive potential; thus, by producing large number
of eggs, it ensures its survival and existence.
Economic importance Ascaris
❖ It causes disease e.g. anaemiaie. ascariasis
❖ Used for biological study
❖ May lead to ulcers as they bore intestinal wall
❖ May lead to anemia
❖ May cause elephantiasis e.g. filarial worm
