Learn the classification of living things for Form Two, including the major kingdoms, characteristics of organisms, and examples of each group.

CLASSIFICATION OF LIVING THINGS

KINGDOM ANIMALIA

Kingdom Animalia is composed of a wide variety of animals. It consists of multicellular eukaryotic organisms with a high level of tissue differentiation and specialized organs.

Animals are placed into two major groups based on the presence or absence of a notochord at least at one stage of their development:

1. Chordates

Chordates are animals that possess a notochord at least at one stage of their development.

2. Non-chordates

Non-chordates are animals that lack a notochord.

What is a Notochord?

A notochord is a slender, supporting, rod-like structure that runs longitudinally along the dorsal side of an animal, especially during the embryonic stage of development.

The notochord may persist throughout life in some animals, while in others it may be replaced by a backbone or vertebral column as the animal develops.

GENERAL CHARACTERISTICS OF KINGDOM ANIMALIA

The general characteristics of Kingdom Animalia include:

1. They are multicellular organisms
   This means that their bodies are made up of more than one cell.

2. They are eukaryotic organisms
   Their cells possess a clearly defined nucleus and membrane-bound organelles.

3. They have a heterotrophic mode of nutrition
   This means that they depend on other organisms as a source of food.

4. They show locomotion
   Most animals are capable of moving from one place to another, although the degree of movement varies among different animals.

5. Their cells lack a cell wall and chlorophyll
   Unlike plants, animal cells do not have a cell wall or chlorophyll.

6. They possess a nervous system
   Most animals have a nervous system that helps them respond to changes in their surroundings. Sponges are an exception because they lack a true nervous system.

7. Most have specialized body organs
   Animals generally have specialized organs and tissues that perform different functions.

8. Most digest food internally
   Food is generally digested inside the gut, and carbohydrates are commonly stored in the form of glycogen.

9. Most animals are triploblastic
   Their bodies develop from three main embryonic layers: ectoderm, mesoderm, and endoderm.

10. Most animals are bilaterally symmetrical
    This means that their bodies can be divided longitudinally into two approximately equal and similar halves.

DISTINCTIVE FEATURES OF KINGDOM ANIMALIA

The distinctive features of Kingdom Animalia include:

1. Internal digestion of food
   Most animals digest their food internally in the gut and store carbohydrates in the form of glycogen.

2. Presence of a nervous system
   Most animals possess a nervous system that helps them detect and respond to changes in their surroundings. Sponges are an exception.

3. Heterotrophic nutrition
   Animals cannot manufacture their own food. They depend on other organisms for food and nutrients.

4. Locomotion
   Most animals can move from one place to another. Movement helps them search for food and mates and escape from danger.

MAJOR PHYLA OF KINGDOM ANIMALIA

The major phyla of Kingdom Animalia include the following:

1. Phylum Platyhelminthes — Flatworms

Platyhelminthes are commonly known as flatworms.

Examples include:

• Liver flukes

• Blood flukes

• Tapeworms

• Planaria

2. Phylum Aschelminthes — Nematoda

Members of this group are commonly referred to as roundworms.

Examples include:

• Hookworms

• Ascaris (roundworms)

3. Phylum Annelida

Annelids are segmented worms. Their bodies are divided into a series of segments.

Examples include:

• Earthworms

• Leeches

• Sabella

• Lugworms

• Ragworms

4. Phylum Arthropoda

Arthropods are animals with jointed appendages and an external skeleton.

Examples include:

• Ticks

• Spiders

• Scorpions

• Butterflies

• Crabs

• Houseflies

• Bees

• Grasshoppers

• Cockroaches

5. Phylum Chordata

Chordates are animals that possess a notochord at least at some stage of their development. In vertebrates, the notochord is associated with the development of the vertebral column.

Examples include:

• Humans

• Rats

• Cows

• Dogs

• Cats

• Donkeys

• Fish

• Lions

• Lizards

• Elephants

• Leopards

• Seals

• Bats

• Hens

• Snakes

• Frogs

OTHER PHYLA OF KINGDOM ANIMALIA

Other important phyla of Kingdom Animalia include:

1. Cnidaria

Example: Hydra

2. Porifera

Example: Sponges

3. Ctenophora

Example: Comb jellies

4. Mollusca

Example: Snails

5. Echinodermata

Example: Starfish

SUMMARY OF CLASSIFICATION OF KINGDOM ANIMALIA

Kingdom Animalia consists of multicellular, eukaryotic, heterotrophic organisms. Animal cells do not have cell walls or chlorophyll, and most animals are capable of locomotion.

Animals can broadly be divided into chordates and non-chordates according to the presence or absence of a notochord.

The notochord is a supporting rod-like structure found along the dorsal side of chordates, particularly during embryonic development.

Important characteristics of animals include multicellular organization, heterotrophic nutrition, locomotion, specialized tissues and organs, internal digestion, and the presence of a nervous system in most groups.

Major and other important animal phyla include Platyhelminthes, Aschelminthes (Nematoda), Annelida, Arthropoda, Chordata, Cnidaria, Porifera, Ctenophora, Mollusca, and Echinodermata.

Understanding the characteristics and examples of each phylum helps students understand how living organisms are classified according to their similarities, differences, and structural features.

1. PHYLUM PLATYHELMINTHES (FLATWORMS)

• Platyhelminthes means “flatworms.”

• They are called flatworms due to their flat bodies. They are also known as “solid worms” or “acoelomates.”

• Acoelomates are animals which do not have a coelom (body cavity).

• They live in fresh water, salt water, and some inhabit terrestrial habitats.

• Some are free-living, while others are parasitic.

• Phylum Platyhelminthes has four classes as follows:

  a) Class Turbellaria
  b) Class Trematoda
  c) Class Cestoda
  d) Class Monogenea

General Characteristics of Platyhelminthes

i. Their bodies are soft, ribbon-shaped, and dorsoventrally flattened.

ii. They are bilaterally symmetrical.

iii. They are triploblastic, with three layers: ectoderm, mesoderm, and endoderm.

iv. They have no body cavity (coelom).

v. They live in fresh water, marine water, and others are parasitic.

vi. They lack a circulatory system, skeletal system, and respiratory system.

vii. They use flame cells in excretion and osmoregulation.

viii. They have a nervous system with a pair of anterior ganglia or a nerve ring.

Distinctive Characteristics of Platyhelminthes

i. They have unsegmented bodies, except cestodes.

ii. They have an incomplete digestive system. Their digestive cavity has a single opening (mouth) and lacks an anus, except members of Class Cestoda.

iii. They are hermaphrodites (monoecious), that is, they have both male and female sex organs.

iv. They have no body cavity (coelom).

a) CLASS TURBELLARIA

• Consists of free-living flatworms.

• They are ciliated on the underside (ventral part) of their bodies.

• They are nocturnal animals (they are inactive during the daytime). They hide under stones during the day and emerge at night to get food.

• They are carnivorous animals, feeding on other organisms such as small worms, crustaceans, and dead bodies of large organisms.

• Example: Planaria.

Distinctive Features of Turbellaria

i. They are aquatic organisms living in fresh water.

ii. Their ventral part (underside of the body) is covered by cilia, which helps them to move in water and on stone surfaces.

iii. They have an incomplete digestive system with only a mouth opening and no anus. Undigested food materials leave and enter the body through the same opening (mouth).

iv. They are hermaphrodites with cross-fertilization.

v. They reproduce asexually by binary fission (splitting into two halves, each of which develops to form a complete organism).

a) CLASS TREMATODA

• This class includes parasitic flatworms (ectoparasites and endoparasites).

• Examples of members belonging to this class are:

  • Blood flukes (Schistosoma species), such as:

    • Schistosoma haematobium

    • Schistosoma mansoni

    • Schistosoma japonicum, which affect humans

    • Schistosoma bovis, which affects ruminants

  • Liver flukes (Fasciola species):

    • Fasciola hepatica

    • Fasciola gigantica

• They are parasites of herbivores (sheep, goats, and cattle) and occasionally affect humans.

• Adult Fasciola species live in the bile duct of herbivores (sheep, goats, and cattle) and occasionally in humans.

Diagram of Trematodes

Liver fluke (Fasciola) and Blood fluke (Schistosoma)

Distinctive Features of Trematodes

i. They have a complex life cycle involving two hosts:

• Primary host (vertebrates) – sexual reproduction takes place.

• Intermediate host (molluscs, usually snails) – asexual reproduction occurs.

ii. They have no cilia but have suckers (oral sucker and ventral sucker) for feeding and an external cuticle for attachment.

iii. They have digestive, excretory, nervous, and genital systems.

iv. They are hermaphrodites (monoecious), except the genus Schistosoma.

v. Reproduction involves cross-fertilization.

vi. They have an unsegmented body.

vii. Their bodies are dorsoventrally flattened (leaf-like).

Class monogonea

The members include the skin flukes found on skin or gills  of fresh-water fish and marine water fish.exampleDactylogyrus vastator parasite of fish which attacks gills Gyrodactyllus salaris an ectoparasite living on the body surface of fresh water fish

Distinctive Features

• They have a large posterior sucker armed with large hooks for attachment to the gills or skin of the host.

• They lack or have a weak oral sucker.

• They have a direct life cycle and do not have an intermediate host. They have a free-living, ciliated larva called the onchomiracidium.

Economic Importance of Trematodes

i. They cause diseases in livestock and humans. For example, Schistosoma species cause Schistosomiasis (bilharzia), while Fasciola species cause Fasciolosis in livestock.

ii. They cause damage to internal organs (liver) of humans and livestock.

iii. They are used in biological studies as specimens.

c) CLASS CESTODA (TAPEWORMS)

• This class consists of parasitic flatworms living inside the bodies of the host (endoparasites).

• Examples of members belonging to this class are:

  • Taenia solium (Pork tapeworm) – commonly affects pigs and occasionally humans. Its scolex has hooks, a rostellum, and four suckers.

  • Taenia saginata (Beef tapeworm) – commonly affects cattle and occasionally humans. Its scolex has no hooks or rostellum but has four suckers.

Distinctive Features

i. They are endoparasitic flatworms.

ii. They have segmented bodies. The segments are called proglottids and are capable of reproducing sexually. The segmented body made of proglottids is called a strobila.

iii. They have suckers (one or more) and hooks for attachment to the intestinal wall of the host. The suckers and hooks together make the scolex (head) of a tapeworm.

iv. They lack a mouth or gut cavity; therefore, they absorb digested food through the cuticle.

v. Their life cycle involves two hosts (primary and secondary hosts).

vi. Their outer surface is not covered with cilia.

TAPEWORM

• The adult tapeworm lives in the intestine of humans and pigs, where it attaches itself with hooks and suckers. It absorbs the host's partly digested food through its skin.

• A tapeworm is composed of scolex (suckers and hooks), rostellum, neck, and proglottids (reproductive structures).

• The proglottids have no fixed number and are of different ages.

• The new proglottids are towards the head region, while older ones are towards the posterior end. Each proglottid reproduces sexually.

• For species that infect humans, mature proglottids (gravid proglottids) detach from the parent and leave through the anus and can be seen in pants.

NOTE:

• Human beings are infected when they eat raw (undercooked) meat or salad containing eggs of the parasite.

• When the eggs are ingested, they hatch and develop into a larva which attaches to the stomach wall, where it develops into a new parasite.

• Some larvae may travel to affect other organs such as the brain, where they develop into a cyst, which leads to many complications such as seizures (unconsciousness).

• The cyst also affects systems such as the nervous system, leading to a condition called Neurocysticercosis.

• Cattle and pigs are affected by ingesting vegetation contaminated with eggs or gravid proglottids.

• An intestinal infection caused by adult tapeworms is called Taeniasis.

Economic importance of Tapeworm

ü  Tapeworms are parasitic infecting human being and livestock such as pigs and cattle leading to great economic loses

ü  Used in scientific research as specimens.

         Control

Ø  Inspecting meat for the presence of tapeworms

Ø  Proper sanitation to ensure that cattle or pigs do not ingest tapeworm egg from human feaces.

Ø  Proper preparation (cooking) of meat (beef and pork) and salads.