Download diversity of animals

Natural Science: Grade 7
Life and Living: Diversity of Animals
DIVERSITY OF ANIMALS
Some scientists have estimated that there are up to 7,7 million species of animals on Earth,
with millions more still to be discovered.
South Africa is fortunate to have the largest variety of animals on the planet.
Both animals and plants are different to organisms in the other Kingdoms as they are multicellular. Organisms in the Animal Kingdom (Anamalia) are different to the organisms in the
Plant Kingdom (Plantae) because they cannot make their own food. They are heterotrophs.
Animals can be either warm-blooded or cold-blooded, depending on whether they can
regulate their body temperature.
A cold-blooded animal varies its body temperature according to the temperature of the
environment. Its body temperature is usually a few degrees warmer than the surrounding
environment.
A Snake is a Cold-Blooded Animal
A warm-blooded animal is one whose body temperature is controlled internally and has a
constant body temperature. It uses energy to do this, for example by shivering when cold and
sweating when hot.
A Cat is a Warm-Blooded Animal
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Natural Science: Grade 7
Life and Living: Diversity of Animals
Classification of Animals
Animals are classified on the basis of whether they have a vertebral column, i.e., vertebrates,
or not, i.e., invertebrates.
The vertebral column is a chain of small bones including the vertebrae (singular: vertebra),
which are joined together. The spinal cord is a collection of nerves running from the brain
down the back, through the vertebral column. The vertebral column consists of the vertebrae
and the spinal cord.
Vertebrates
Vertebrates belong to a large Phylum called Chordata. There are around 60,000 species of
vertebrates.
All vertebrates have certain distinguishing characteristics:
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They have a vertebral column.
They have an exoskeleton made of chitin.
They have a skull, which contains a brain.
They are bilaterally symmetrical. This means that they have two equal halves from
the head down the vertebral column, dividing the body into a left and right side. This
assists with co-ordination of movement.
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Natural Science: Grade 7
Life and Living: Diversity of Animals
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They have two pairs of appendages for locomotion (movement). These are limbs
which have been modified depending on the type of movement, for example, flying,
swimming or walking.
They reproduce sexually.
They can be warm or cold-blooded.
Vertebrates are further classified into the following five classes, on the basis of distinguishing
characteristics:
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Mammals
Birds
Fish
Reptiles
Amphibians
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Natural Science: Grade 7
Life and Living: Diversity of Animals
Mammalia (Mammals)
There are around 5,500 species of mammals on planet Earth.
Characteristics
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Mammals are warm-blooded.
Most live on land and some live in water.
They have fur or hair covering their skin.
They breathe using their lungs.
They have four limbs, usually modified, for example, on land as legs, and in water as
limbs.
Mammals are viviparous, meaning that the female gives birth to live young.
Fertilisation occurs internally.
Between 1 and 5 offspring are usually born.
The mother feeds her young with milk from her mammary glands and there is
extended parental care.
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Examples: cows, horses, lions, antelope, cats, dolphins, whales, bats, kangaroos, giraffes.
Mammals on Land
Mammal in the Water
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Newly Born Foal
Foal Feeding from its Mother
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Natural Science: Grade 7
Life and Living: Diversity of Animals
Aves (Birds)
There are around 10,000 species of birds found on Earth. 858 species are found in South
Africa, with 31 species being endemic. The coast is home to a variety of seabirds, of which
some are endemic and some migrate from Europe. The largest bird, the ostrich, is found in
South Africa.
Characteristics
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Birds are warm-blooded.
Most live on land and in the air.
Their legs are covered with scales and their bodies with feathers.
They breathe using their lungs.
They have a beak and no teeth.
Their limbs have been modified into wings for flying. Some are adapted to swim, for
example, the penguin.
Nearly all birds can fly, with the exception of about forty species, for example the
ostrich and the penguin.
Birds are oviparous, meaning that they lay eggs. The eggs are protected with a hard
shell and lined with a thin membrane.
Fertilisation is internal.
Between 1 and 10 eggs are usually laid.
Parental care is present.
Examples: Eagles, falcons, vultures, owls, sparrows, kingfishers, swallows, ducks.
Birds’ Limbs Modified for Flying
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Bird Feeding its Young
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Both the Ostrich and Penguin cannot fly
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Life and Living: Diversity of Animals
The Ostrich and The Penguin Cannot Fly
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Natural Science: Grade 7
Life and Living: Diversity of Animals
Pisces (Fish)
There are more fish species than any other vertebrate on the planet, with over 30,000 known
species. Around 250 new species are discovered each year. Fish are found in both marine
(58%) and freshwater habitats (41%). The other 1% migrates between the two habitats to
spawn.
The South African coast has many species of fish; however, there are limited numbers of
freshwater fish.
Fish are classified as bony, cartilaginous or jawless.
Characteristics
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Fish are cold-blooded.
They live in water.
Their bodies are covered with scales.
They breathe using gills to extract oxygen from the water.
Their limbs are modified as fins for swimming.
Fish are oviparous (lay eggs).
Fertilisation is external.
They lay thousands of eggs at a time.
There is no parental care.
Examples: trout, salmon, dorado, mackerel, hake, dorado, halibut, tuna, marlin.
Various Fish Species
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Natural Science: Grade 7
Life and Living: Diversity of Animals
Reptilia (Reptiles)
There are over 10,000 species of reptiles, of which the majority are lizards, followed by
snakes. In South Africa, more than 400 species of reptiles are found, of which 130 species are
snakes.
Characteristics
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Reptiles are cold-blooded.
Most live on land, but some spend time in the water.
Their bodies are covered with scales and in some cases these have been adapted to
form large plates that make a shell, for example, turtles and tortoises.
They breathe using lungs.
Most reptiles have four legs. Reptiles that live on land move using their legs. Reptiles
that live in water use flippers and their tails to move. Snakes and some lizards do not
have limbs.
Reptiles are oviparous (lay eggs) or ovoviviparous, meaning that they produce eggs
that are hatched within the body, so that the young are born live, but without
attachment to a placenta.
Fertilisation is internal.
They lay thousands of eggs at a time.
There is no parental care.
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Life and Living: Diversity of Animals
Examples: lizards, chameleons, snakes, crocodiles, alligators, turtles.
Chameleon
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Turtle Laying Eggs
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Natural Science: Grade 7
Life and Living: Diversity of Animals
Amphibia (Amphibians)
There are about 7000 species of amphibians, divided into three main groups, depending on
whether they have a tail or limbs. Around 90% of amphibians are frogs. The only amphibians
found in South Africa are frogs and toads.
The word ‘amphibian’ means ‘two lives’, referring to how they live both on land and water.
Characteristics
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Amphibians are cold-blooded.
They live in the water when they are young and mainly on land as adults, returning to
the water to breed.
They go through a body change known as metamorphosis when growing into an
adult.
Adult amphibians breathe using their lungs, while tadpoles use gills.
They have four legs which are modified. They move around by using their legs.
Movement includes walking, swimming and jumping.
Amphibians are oviparous (lay eggs).
Fertilisation is external.
They lay hundreds of eggs at a time.
There is no parental care.
Examples: frogs, toads, salamanders, caecilians.
Toad
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Salamander
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Life and Living: Diversity of Animals
Invertebrates
Invertebrates make up around 98% of the known animal species on Earth.
All invertebrates have one characteristic in common – they do not have a vertebral column.
Invertebrates are divided into Phyla Arthropoda and Phyla Mollusca, on the basis of
distinguishing characteristics, such as whether they have a hard or a soft body.
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Natural Science: Grade 7
Life and Living: Diversity of Animals
Arthropoda
‘Arthro’ means ‘jointed legs’.
Characteristics
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They have an exoskeleton (external skeleton)
made of chitin (a tough protective coating).
Their bodies are divided into segments.
They have jointed legs.
Some have appendages (an arm, leg or a tail that
is joined to the body).
Discarded Skeleton of Dragonfly Nymph
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Arthropods are further sub-divided into 5 main Classes, as shown in the diagram below.
Insecta (Insects)
This is the largest class of arthropods, with just under a million known species. Around
100,000 species are found in South Africa.
Characteristics
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They all have 6 legs, often found on their thorax.
They often have wings and are the only arthropods to have wings.
They have three body divisions – the head, thorax and abdomen.
They breathe through openings down the side of their bodies, called spiracles. Carbon
dioxide is also excreted through these spiracles.
They have a pair of antennae with a pair of compound eyes having many lenses.
They shed their exoskeleton when they are growing.
Insects can be divided into crawling insects, e.g., ants, and flying insects, e.g., flies.
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Examples: flies, locusts, beetles, ants, butterflies, bees, wasps, cockroaches.
A Variety of Insects
Beetle Laying Eggs
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Butterfly
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Arachnia (Arachnids)
There are over 100,000 species of arachnids, of which 2000 are found in South Africa.
Arachnid in Greek means ‘spider’.
Characteristics
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They all have 8 legs, i.e., 4 pairs of jointed legs used for walking.
They have two body divisions – the abdomen and the cephalothorax (head and thorax
combined).
Arachnids differ from other insects in that they do not have antennae.
They spin webs to catch their prey and to store their eggs.
Arachnids also have spiracles on their abdomens to take in air.
Examples: spiders, ticks, scorpions, mites.
Spider in Web
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Scorpion
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Life and Living: Diversity of Animals
Crustacea (Crustaceans)
Crustacea are a large group, with around 67,000 species. There are around 2,300 species
found in South Africa.
Crustacea in Latin means ‘shell’ or ‘crust’.
Characteristics
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Crustacea have 5 pairs of legs. The front pair is adapted to form pincers.
They have two body divisions – the abdomen and the cephalothorax (head and thorax
combined).
They have antennae and compound eyes on stalks.
As they live in water, they breathe through gills.
Examples: crabs, lobsters, crayfish, prawns, shrimps, krill, barnacles.
Lobster
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Barnacles
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Natural Science: Grade 7
Life and Living: Diversity of Animals
Chilopoda
There are an estimated 8,000 species, although only around 3,000 have been described.
Chilopoda means ‘lip foot’ in Greek.
Characteristics
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Chilopoda have one pair of legs per body segment.
Their bodies are divided into a head and a trunk.
They breathe through openings in the segments.
They have antennae and simple eyes.
They have sharp, poisonous mouthpieces (fangs).
Examples include: centipedes.
Centipede
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Natural Science: Grade 7
Life and Living: Diversity of Animals
Diplopoda
There are estimated to be over 12,000 species of diplopoda.
The name diplopoda in Greek means ‘double foot’.
Characteristics
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Diplopoda have two pairs of legs per body segment (except the first three segments).
The segments behind the head have holes for breathing.
Their bodies may be flat or cylindrical.
Their bodies are divided into a head and a trunk.
They breathe through openings in the segments.
They have simple eyes.
Examples include: millipedes
Millipede
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Natural Science: Grade 7
Life and Living: Diversity of Animals
Mollusca (Molluscs)
Invertebrates whose bodies are not divided into segments are known as ‘molluscs’.
Mollusca means ‘having a soft body’.
There are over 80,000 species of molluscs. Both marines and non-marine molluscs are found
in South Africa.
Characteristics
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Molluscs have a hydrostatic skeleton, filled with fluid to keep the mollusc firm.
They have soft, unsegmented bodies.
Their bodies are covered with moist skin.
Some have an outer shell to protect their soft bodies, for example, snails.
Some have an inner shell, for example, the octopus and the cuttlefish.
Slugs do not have a shell.
Most molluscs live in water.
Examples: mussels, oysters, octopi, garden snails, limpets, barnacles, cuttlefish.
Snail
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Octopus
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The diagram of a snail shows it has three main body parts – the head, the foot and the hump,
which is covered by a shell. There are two pairs of tentacles on the head, which have simple
eyes on the end of the tentacles.
The snail produces slime, which enables it to move with its muscular foot. It breathes through
gills found in the mantle, which is a layer of skin below the snail’s shell.
The snail also has a T-shaped tongue called the radula.
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