There are millions of animals in this world. Despite their diversity, they all have some characteristics that are similar between groups of animals and this is what binds them together.
By the end of this lesson, you’ll be able to
Animals are grouped under the Kingdom Animalia or the Animal Kingdom. Within the Animal Kingdom, they are classified into different groups. This helps us to understand their characteristics, as well as their differences with other organisms.
All organisms in the Animal Kingdom are eukaryotes. They are all multicellular. They cannot make their own food.
Broadly, there are two categories: vertebrates and invertebrates.
Vertebrates are animals with backbones. These are mammals, birds, fish, reptiles, and amphibians. They are all part of the phylum 'Chordata' (having spinal cord).
Invertebrates are animals without backbones. They are all part of the phylum 'Arthropoda'. Two common classes in this phylum are – arachnids (spiders) and insects.
They are warm-blooded animals which allows them to inhabit both cold and hot habitats. They can regulate their body temperature to live in deserts (camels), glaciers (polar bears) and oceans (whales).
They give birth to their young ones.
They have hair or fur.
Mammal mothers nurse their babies with milk.
All fish are cold-blooded. This means they are unable to regulate their body temperature, relying solely on the external environment for temperature regulation. The body temperature of fish changes as the environment’s temperature changes.
They live in water their entire lives. While all fish live in water, not everything that lives in water is a fish. For example, whales and dolphins are mammals, turtles are reptiles.
They have gills to breathe. Gills absorb oxygen from water and release carbon dioxide, which allows them to breathe underwater.
Their body is covered with scales.
They have fins attached to help them move through the water.
When male and female fish mate, the eggs often meet the sperm in the water. This is called external fertilization.
Examples of fish – herring (seawater fish) and pike (freshwater fish).
It is believed birds evolved from dinosaurs during the Mesozoic era. They share some characteristics with other animal classes, including a skeletal backbone, a four-chambered heart, and being warm-blooded.
Their bodies are covered with feathers.
They do not have teeth but use their beaks to eat food.
They are oviparous which means they lay eggs to develop their young ones.
Their front limbs are adapted as wings, although not all birds fly.
Birds breathe using lungs.
Examples of birds – eagle, hummingbird, parrot.
In evolutionary terms, reptiles are intermediate between amphibians and mammals.
They are cold-blooded animals.
Their bodies are covered in hard scales but have no hair or fur. The scales of the reptiles develop as surface cells filled with keratin.
They are tetrapods which means they have either four limbs (like turtles and crocodiles) or are descended from four-limbed animals (like snakes).
They breathe using lungs.
They have a three-chambered heart except for alligators and crocodiles which have a four-chambered heart.
They are amniote animals which means that the eggs laid by females contain an elastic sac within which the embryo develops. Most reptiles are oviparous and lay hard-shelled eggs.
Reptiles rely on their vision than any other sense organs. They don’t have external ears instead they have eardrums near the eyes and closed to the skin surface.
Amphibians are cold-blooded animals.
They have very thin skin which must always be kept wet because they breathe through their skin.
Though they have small lungs they aren’t used much.
Fertilization is external and takes place in the water. The eggs are covered with jelly to protect them.
Their larvae are called tadpoles which are aquatic. They metamorphose into the adult amphibian which lives on land but always near water.
Examples of amphibians – frog and newt.
Arachnids are commonly called spiders. It also includes some non-spider like bugs such as scorpions and ticks.
They have two main body sections called the cephalothorax and the abdomen.
They have eight legs – four on each side.
They have eight eyes. These are simple eyes so their vision is not as sharp as that of insects.
They do not have antennae. They do have two pincers on the front that act as a mouth.
They do not have wings.
They have fangs to inject poison for paralysis of their prey.
They can spin webs for catching and holding their prey.
They have an exoskeleton and lay eggs.
They have a segmented body consisting of three sections – head, thorax, and abdomen.
They have an intricate internal system that includes a brain, a nervous system, a heart, a stomach or gut and breathing tubes referred to as tracheae.
They have a hard-external covering made of something called chitin.
They have six legs – one pair on each body segment.
They have wings connected to the thorax and can fly.
They have a pair of antennae on their head and use them as feelers.
They have compound eyes; therefore, they have sharper vision.
They are born from eggs. Young insects are called nymphs. As insects grow, they get a new hard covering by getting rid of the old covering and growing a new one. This process is called molting.
Examples of insects are bees, ants, wasps, and termites.
