The Kingdom Animalia is a large group that consists of eukaryotic, multicellular organisms that are heterotrophic in nature. As such, they obtain their nutrition from external sources.

Although they are unable to produce their own food, which is one of the main defining characteristics of plants, animal cells lack a cell wall that is present in plant cells.

Kingdom Animalia constitutes all animals.

Amongst the five kingdoms, the largest kingdom is the animal kingdom. Animals are multicellular eukaryotes. However, like plants, they do not possess chlorophyll or a cell wall.

Therefore, members of the animal kingdom exhibit a heterotrophic mode of nutrition. Kingdom Animalia has been classified into ten different subphyla based on their body design or differentiation.

The different phylum of the animal kingdom are as follows:

  1. Porifera
  2. Coelenterata (Cnidaria)
  3. Platyhelminthes
  4. Nematoda
  5. Annelida
  6. Arthropoda
  7. Mollusca
  8. Echinodermata
  9. Hemichordata
  10. Chordata


i. They are multicelular eukartyotes.

ii. Their cells have no cell wall.

iii. They have no chlorophyll.

iv. Heterotrophic mode of nutrition.

v. Posses nervous system.

Two main groups

Vertebrates have bony vertebral column (back bone) that encloses the spinal cord.

Invertebrates have no vertebral column.

Phylum of Animalia Kingdom

A). Phylum Porifera

These are sponges. This is the only phylum within the subkingdom parazoa.

Main features are:-

i. Always sessile, i.e. Permanently attached to the rocks or seabed.(do not show movement).

ii. Have calcareous skeleton.

iii. Occur as a colony.

iv. Body contains two layers, i.e. Outer (epithelial cells) and Inner (collar cells).

v. Cavity lined by flagellated collar cells for creating water currents.

vi. Reproduction mainly asexual through budding

vii. Examples are ascon, syncon, etc.

B). Phylum Cnidaria (Coelenterata).

Main features

i. Single opening for taking in food and removing undigested materials.

ii. Are radically symmetrical.

iii. Are carnivores.

iv. Mouth is surrounded by tentacles used for catching and piercing the prey.

v. Have stinging cells (cnidoblast) for killing or paralyzing the prey.

vi. Are soft and jelly like.

vii. Reproduce asexually by budding.

viii. Have diploblastic body wall (made up of two layers of cells, i.e. Ectoderm and endoderm).

ix. Body forms exists in two forms polyp (sensile) and medusa (free swimming umbrella or bell shape).

The phylum has three classes

i). Class Hydrozoa.

They are hydra like in appearance and live attached to water plants and rocks in ponds, lakes and rivers. Examples are Hydra, Obelia, Physalia, etc.

ii). Class Scyphozoa.

Examples are Aurelia, Jelly fish, etc.

iii). Class anthozoa.

Examples are Sea Anemone.

C). Phylum Platyhelminthes (Flat worms).

They are also called acoelomates because they do not have a coelom (Fluid filled body cavity).

Main features

i. Are ribbon shaped and soft bodied.

ii. Bilaterally symmetrical.

iii. Are hermaphrodite.

iv. Dorso-Ventrally flattened.

v. Are triploblastic, i.e. Made up of three layers, i.e. Ectoderm, mesoderm and endoderm.

vi. Live in marine and frosh water environment.

vii. Most of them are parasitic while some are free living, i.e. Planaria.

viii. Single opening for taking in food and removing undigested materials.

ix. Use flame cells for excretion and osmoregulation.

x. Lack a circulatory system. .

The phylum has three classes.

i). Class Turbellaria.

These are free living flatworms. They are usually ciliated on the ventral (undreside), eg. Planaria.

ii). Class Trematoda.

These include ectoparasites and endoparasites. They have no cilia or succurs for attachment. Examples are Liver fluke, (Fasciola hepatica,) Blood fluke (Schistosoma).

iii). Class Cestoda.

These are endoparasitic worms.

Some have hook and suckers.

Their bodies are divided into segments called proglottids.

Examples are tape worms: Taenia solium found in pigs. Taenia saginata found in cattle.

D). Phylum Aschelminthes-Nematoda (Round worms).

Main features

i. Are un-segmented, slender cylindrical body

ii. They lack circulatory system.

iii. Have pseudocoelom for absorption of food and also serves as hydrostatic skeleton.

iv. Bilaterally symmetrical

v. Have two openings, i.e. Mouth and anus connected by a complete digestive canal.

vi. Have a narrow body, which is pointed at both ends.

vii. Most are parasites while some are free living.

viii. Are round in cross section

ix. Sexual reproduction where males are smaller than females

x. Bodies have cuticle for protection, i.e. From desiccation in free living and from being digested for those that live as parasite in the gut of vertebrates.

xi. Examples are Ascaris (in gut of human and pigs), Hook worms.

E). Phylum Annelida.

Main features

i. Are segmented worms, where by anterior segment carries the head (brain and mouth) while the posterior segment carries the anus.

ii. Have primitive brain and nerves.

iii. Have well develop circulatory, digestive and excretory systems.

iv. Have true coelom that lies between the body wall and the gut.

v. The coelom helps in absorption of food and serves as hydrostatic skeleton.

vi. They use nephridia for excretion and osmoregulation.

vii. Are bilaterally symmetrical.

viii. Live in a sea water, fresh water or land. (Aquatic use gills while terrestrial use epidermis for gaseous exchange.

ix. Parasitic worms live in the bodies of other organisms.

x. They show metamerism, i.e. The body has many segments (septa), and in each is a number of complete organs (chaetae or setae).

The phylum has three classes.

i). Class Polychaeta.

Have many Chaetae (bristles) and are mostly marine.

Have separate sexes.

Examples are Sabella, Arenicola, Nereis, Lugworm, Funworm, etc.

ii). Class Oligochaeta.

They have fewer chaetae and are both fresh water and marine water.

They are haemophrodite. However sex organs are located in such a way that a worm cannot fertilize its own eggs, but they can fertilize each other at the same time

Examples are Earthworm (Lumbricus)

iii). Class Hirudinea (Leech).

Have no chaetae.

They poses suckers on both anterior and posterior ends.

Some are ectoparasite.

Examples are Hirudo, Glossiphonia, Leech, etc.

F). Phylum Mollusca.

Main features

i. Have soft unsegmented body.

ii. Upper part of the body is called visceral mass, containing digestive, circulatory, excretory, respiratory and reproductive system.

iii. The head has mouth and tentacles, each of the upper tentacle is tipped by a little black eye.

iv. The lower part has muscular flat foot for locomotion.

v. All mollusca except bivalves possess a unique rasping tongue called radula.

vi. Most have shells to protect them from predators and desiccation.

vii. They are either marine, fresh water or terrestrial.

The phylum has two main classes.

i). Class Gastropoda (Snail and Slugs)

Have large flat foot.

The visceral hump (mass) rotates during development resulting in coiling of the shell.

Examples are Helix, Buccinum, Testacella, etc.

ii). Class Cephalopoda.

The shell is internal and reduced or absent. They protect themselves by their colouration or by discharge of coloured materials.

They have 8 to 10 sucker bearing tentacles.

Examples are Octopus, Sepia, etc.

G). Phylum Arthropoda.

Arthropods are the most successful of all animals, they live on land, seawater, freshwater and air.

About two thirds of all named animals in the world are arthropods.

Main features.

i. Have jointed appendages.

ii. Posses exoskeleton made up of chitin, i.e. nitrogen containing polysaccharide.

iii. Their chitinous cuticle is shed periodically to allow growth.

iv. The process of shedding the cuticle is known as moulting or ecdysis.

v. Gases exchange through trachea, gills or book lungs, i.e. Terrestrial use tracheoles while aquatic use gills.

vi. They are metamerically segmented, i.e. Each segment has a complete set of organs.

vii. Mouth part adapted for either chewing, sucking or piercing and sucking.

viii. Some lay eggs while others produce young ones.

The Phylum has five main classes.

i). Class Arachnida.

Have four pairs of legs.

Cephalothorax, i.e. Their thorax and head is joined together.

Most of them are parasites.

They lack antennae.

They use book lungs for gaseous exchange.

Examples are Ticks, Mites, Spiders, Scorpions.

ii). Class Crustacea.

Cephalothorax, i.e. Head and thorax are fused together.

Most of them are aquatic, a few are terrestrial.

Examples are Lobsters, Woodlouse, Prawn, Shrimp, Crabs, etc.

iii). Class Chilopoda.

Have segmented bodies.

Have one pair of legs in each segment.

They are carnivorous and mainly feed on insects.

Example is Centipedes.

iv). Class Diplopoda.

They have segmented bodies.

Have two pairs of legs on each segment.

They live in dark and moist areas.

They feed on plants.

Example is Millipedes.

v)Class Insecta.

They are the most abundant of the arthropods.

Have 3 pairs of legs, each pair arising from thoracic segment.

Have 2 pairs of wings.

Have one pair of antennae on the head.

Bodies divided into three parts, i.e. Head, thorax and abdomen.

Have one pair of well developed compound eyes.

Gaseous exchange through trachea (spiracles).

Their exoskeleton is water proof.

Examples are Cockroach, House fly, Mosquito, Butterfly, Tsetsefly, Locust, etc.

 Importance of insects to human being.

-Pollination, ie. Bees and butterflies.

-Source of food, ie. Honey from bees, and some insects are edible.

-Wax from bees is used to manufacture candles, lipsticks and polish.

-Biological pests control, e.g. Ladybirds eats aphids.

Some make silk which is used in textile industries.

Harmful effects

– Reduces agricultural harvest, i.e. Locust.

– Some feed on stored grains, i.e. grain weevil

– Destroy buildings and furniture, i.e. Termites

– Diseases vectors like mosquitoes, tsetse flies, house fly, fleas (bubonic plague).

– Spoiling food, i.e. Cockroaches and ants.

 Adaptation of insects

-Insects are found in water, land air and in all climatic regions of the world. This is possible due to the following adaptations.

-Hard exoskeleton which supports them above the ground.

-Water proof waxy layer over the exoskeleton which reduces evaporation.

-Excretion of uric acid which reduces water loss.

-Efficient tracheal system for gaseous exchange.

-Internal fertilization which eliminates the need for water to achieve successful reproduction.

-Ability to fly in most insects which makes it easier for them to spread to new areas or run away from predators.

H). Phylum Echinodermata

These are marine animals.

Echinodermata means spiny skin, i.e. Their skeleton bears spines that project on the surface of the animal.

Adults are radially symmetrical with five arms.

Some are sessile (immobile) at the bottom of the sea.

The larvae (free swimming) is bilaterally symmetrical.

They have well developed coelom.

Their bodies are triploblastic, i.e. Have three layers.

Have separate sexes, fertilization is external, i.e. Sperm and eggs are shed into the surrounding water.

Gaseous exchange is by skin gills.

Have complete digestive system.

Examples are Starfish, Bristle star, Sea urchin, Sea lily, sea cucumber.

I). Phylum Chordata.

These are animals that show highest degree of organization.

Have a dorsal notochord. In vertebrate is called vertebral column.

Have tubular nerve cord.

Have a closed circulatory system.

Have endoskeleton.

Have perforated pharynx or gill slit at least in one stage of their life.

Reproduction is sexual.

The phylum has six main classes.

i). Class Amphibia.

The word Amphibia is a Greek word meaning double life.

-They live both on land and in water.

-Tadpole-aquatic stage breath by gills.

-Adult breathe by skin, buccal cavity and lungs.

-Adult live on land or in water, for breeding they go back to water.

-Have slim moist skin. Toads are drier than frogs.

-Reproduction is sexual:   -Frogs and toads have external fertilization.

-Salamander has internal fertilization.

-Frogs and toads have webbed feet.

-Heart has three chambers, i.e. Two atria and one ventricle.

-Are ectothermic/poikilothermic or cold blooded.

-Examples are Salamander, Frog, Toad, Newt.

ii). Class Chondrichthyes.

These are cartilagious fishes.

Their skeleton is made of cartilages (soft bones).

Have ventral mouth (on the lower side).

The gills are open directly to the outside. Have 5-7 gills on either side of the head.

Have limited range of movement.

Are ectothermic/poikilothermic or cold blooded.

Bodies are covered by tooth like scales.

Examples are Dogfish, Shark, Skates, Rays, etc.

iii). Class Osteichthyes.

These are bony fish.

Bodies covered by overlapping scales, a few are scale-less.

Their skeleton is composed of bones.

Their gills are covered by operculum. Have 4 gills on either side of the head.

Have five sets of fins.

-Pectoral and pelvic fins which are paired.

-Medial fins, ie, Dorsal, ventral and tail fins which are usually single.

Are ectothermic/poikilothermic or cold blooded.

The mouth is located on the dorsal side (front tip of the head).

Have wide range of movement.

Have swim bladder to maintain buoyancy.

The lateral line is present, is used to detect stimulus.

Examples are Tilapia nilotica, Clarias mossambicus, Lung fish, Stickle back.

iv). Class Reptilia.

The word reptilia is a Latin word meaning to crawl.

Some have walking legs while others crawl on the ground.

Are ectothermic/poikilothermic or cold blooded.

They all lay eggs on land. Fertilization is internal

Eggs are covered by membrane known as amnion.

In some species of chameleon eggs are retained in the female oviduct until their hatched.

Some live in waters others live on land.

They have a dry skin with horny scales.

They use lungs for breathing.

Nitrogenous wastes are excreted in the form of uric acid.

Examples are Tortoise, Crocodile, Chameleon, Snake, Lizard.

v). Class Aves (Birds).

Are covered with feathers, to protect and insulate them against heat loss.

They are homoiotherm (warm-blooded or constant body temperature).

Their heart is divided into four cambers.

Have streamlined body adapted for flight.

Have light and hollow bones.

Fore limbs modified into wings for flight.

Hind limbs are used for walking, swimming or perching.

Legs are covered with scales.

Sexes are different and fertilization is internal. They lay eggs.

Have no teeth.

Show parental care for the young ones.

Nitrogenous wastes excreted in the form of semi solid uric acid delivered through cloaca.

Examples are Hen, Dove, Owl, Ostrich, Pigeon, Hawk, Goose, etc.

vi). Class Mammalia.

Are homoiotherm (warm-blooded).

Are vertebrate with four limbs.

Have heterodont teeth.

Reproduction is sexual with internal fertilization.

Develop two types of teeth, i.e. Milk teeth and permanent teeth.

Have mammary glands.

Bodies covered with hair/fur, that acts as insulator and protection from mechanical damage.

Possession of pentadactyl limbs, i.e. Limbs with five digits (phalanges).

Have a diaphragm that separates the thorax and abdomen.

More developed cerebral hemisphere.

The class is divided into sub class.

Marsupials (Metatheria). Embryos are born at very immature stage and grown mainly within a pouch (marsupium) and nourished by mother’s milk, e.g. Kangaroo, Koala bear and opossum.

Monotremes (Prototheria). They lay eggs like those of reptiles, but then give milk to the hatched young using milky glands, e.g. Platypus.

Placental Mammals (Eutheria). Embryos are grown and nourished inside the uterus, e.g. Pig, human being, elephant, etc.

 Placental Mammals are grouped into the following Orders.

Chiroptera these are flying mammals, e.g. Bats

Insectivorous feed on insects, eg. Mole, hedgehogs and shrews.

Herbivorous also called ungulates (hoofed animals), eg. Camel, hippopotamus, rhino, cow, giraffe, etc.

Carnivorous have teeth that are adapted for tearing flesh. Toes have strong claws. Eg. Dog, cats, hyenas, seals, and lion.

Primates have highly developed brain, reaching the highest development in man. Fore limbs modified into hands for grasping and manipulation. They are Omnivores. They include apes, monkeys, baboons and human beings.

Cetacia are hairless mammals that live in water, also called swimming or aquatic mammals. Eg. Dolphins and whale

 Proboscideans, nose modified into a trunk and the two upper teeth are modified into tusks (ivory). Eg elephants and the extinct mammoth.

Economic importance of Animals.

i. Help in pollination, e.g. Insects and some birds.

ii. Used for research work, i.e. Guinea

iii. Used as human food, i.e. Good source of protein.

iv. Used in cultivation, i.e. Oxen for ploughing.

v. Raw materials such as hides and skins for leather industries.

vi. Used for biological pests control, i.e. Cats to control population of rats.

vii. Used for security, i.e. Dogs.

viii. Tourism in national parks and game reserve.

ix. Recycling of nutrients in the soil, e.g. round worm ling in the soil.

x. Improve aeration and drainage in the soil, e.g. Earth worms.

xi. Animal product are also used as food, e.g. Milk, honey, eggs, etc.

xii. Produce carbon dioxide needed by plants for photosynthesis.

xiv. After death they decompose and add soil fertility.

Harmful effects.

i. Some are vectors of disease like Snails (Bilharzia), Mosquitoes (malaria).

ii. Some worms are agents of diseases like filaria that cause Elephantiasis.

iii. Some are parasites like Leech which is an ectoparasite.

Note: Also Check importance of Insects.


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