Classification Of Animal Kingdom

Classification Of Animal Kingdom

Aug 03, 2023, 16:45 IST

The animal kingdom, also known as Animalia, is a diverse group of multicellular organisms that includes insects, fish, birds, and mammals. The animal kingdom is typically classified into several major groups or phyla based on their physical characteristics, behaviours, and evolutionary relationships

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Classification of Animal Kingdom

1. Porifera (sponges):

Asymmetrical or radially symmetrical body

No true tissues or organs

Filter feeders that use specialised cells called choanocytes to trap and ingest food particles

Skeleton made of spicules or a fibrous protein called spongin

Sexual and asexual reproduction

2. Cnidaria (jellyfish, corals, sea anemones):

Radially symmetrical body with tentacles around a central mouth.

Two body forms: polyp (attached to a surface) and medusa (free-swimming)

Body contains specialised stinging cells called cnidocytes that are used for defence and capturing prey

Simple digestive system with a single opening that serves as both mouth and anus.

Nerve net, a decentralised nervous system

Sexual and asexual reproduction

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3. Platyhelminthes (flatworms):

Flattened, ribbon-like body shape,

Bilateral symmetry,

Simple nervous system with a nerve net and two nerve cords,

Simple digestive system present with a single opening that serves as both mouth and anus.

Hermaphroditic or separate sexes

Some of the species included are parasitic, while others are free-living.

Some species can regenerate lost body parts

4. Nematoda (roundworms):

Long, slender, cylindrical shape with tapered ends.

A complete digestive system includes a mouth, intestine, and anus.

No circulatory or respiratory system.

Some are free-living in soil, freshwater, or marine environments, while others are parasitic and can infect plants and animals, including humans.

Sexual reproduction with separate sexes
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5. Annelida (segmented worms):

Segmented body with repeating units called segments.

A complete digestive system with a mouth, intestine, and anus

Closed circulatory system.

Some species have respiratory structures called gills, while others breathe through their skin.

Sexual reproduction with separate sexes

Includes polychaetes (marine worms), oligochaetes (earthworms), and leeches.

6. Mollusca (molluscs):

Soft body with a muscular foot for movement

Mantle, a fleshy layer that covers the body and, in some species, secretes a hard shell made of calcium carbonate

Radula, a feeding structure that scrapes food particles.

Some have gills for respiration, while others breathe through their skin.

An open circulatory system with a heart and blood vessels

Sexual reproduction with separate sexes, some have external fertilisation.

In contrast, others have internal fertilisation,

Including gastropods (snails and slugs), bivalves (clams and oysters), and cephalopods (squids and octopuses)

7. Echinodermata (starfish, sea urchins, sea cucumbers):

Radially symmetrical or pentaradial body shape

Internal skeleton made of plates or spines

Water vascular system, a network of fluid-filled tubes used for movement, gas exchange, and feeding

Simple nervous system present with a nerve ring and radial nerves

Separate sexes with external fertilisation

Regenerative abilities

8. Chordata (vertebrates and their relatives):

Dorsal hollow nerve cord

Notochord is a flexible rod-like structure

Pharyngeal slits or pouches, which may be modified for respiration, feeding, or communication

Post-anal tail, an extension of the body past the anus

Endoskeleton made of bone or cartilage in vertebrates

Complex nervous system with a brain and spinal cord

Closed circulatory system present consisting a heart and blood vessels

Sexual reproduction with internal fertilisation

Some species can regulate body temperature (endothermy)

Chordata is a phylum of animals that includes a diverse range of animals, from fish and birds to humans. Within the phylum, Chordata is three subphyla, divided based on the presence or absence of certain features. These subphyla are

1. Urochordata (tunicates or sea squirts):

Larvae exhibit all chordate features, but adults only retain some.

Sessile filter feeders that attach to surfaces

No proper head or brain

2. Cephalochordata (amphioxus or lancelets):

Retain all the chordate features throughout life.

Marine filter feeders that burrow in the sand.

No proper head or brain

3. Vertebrata (vertebrates):

Possess a vertebral column (backbone)

Skull that protects the brain

Well-developed nervous system with a brain and spinal cord

Endoskeleton with bone or cartilage

Wide range of body forms and habitats

Divided into several classes:

1. Agnatha (jawless fish):

Lack of jaws

Cartilaginous skeleton

No scales

No paired fins

No true stomach

Marine and freshwater habitats

Consists of two extant groups: lampreys and hagfishes

Some species undergo a metamorphosis during their life cycle

2. Chondrichthyes (cartilaginous fish):

Skeleton made of cartilage

Paired fins and five to seven gill slits

Heterocercal tail (upper lobe of the tail is longer than the lower lobe)

Placoid scales (tooth-like scales)

Predominantly marine habitats, with some species found in freshwater

Includes sharks, rays, and chimaeras

3. Osteichthyes (bony fish):

Skeleton made of bone

Scales covering the body

Paired fins and gills covered by an operculum

Swim bladder for buoyancy control

Two-chambered heart

Predominantly aquatic habitats, with some species found in freshwater and a few in marine environments

Includes ray-finned fish and lobe-finned fish (the latter of which includes coelacanths and lungfishes)

4. Amphibia (amphibians):

Smooth, moist skin without scales or feathers

Larvae have gills, adults have lungs for respiration

Three-chambered heart

Most species lay eggs in water and undergo metamorphosis during development

Predominantly terrestrial or semi-aquatic habitats

Includes frogs, toads, salamanders, and caecilians

5. Reptilia (reptiles):

Dry, scaly skin with keratinised epidermal scales,

Lungs for respiration and a three-chambered heart (except for crocodilians, which have a four-chambered heart).

Most species lay eggs on land and undergo little to no metamorphosis during development. Predominantly terrestrial habitats, with some species found in aquatic environments.

Includes turtles, lizards, snakes, crocodilians, and tuataras

6. Aves (birds):

Feathers covering the body and wings for flight

Beak instead of teeth

Lightweight, but strong bones with air sacs for respiration

Four-chambered heart

Hard-shelled eggs

Predominantly terrestrial habitats, but some species are adapted for aquatic or aerial lifestyles

Includes birds of prey, water birds, songbirds, and flightless birds such as ostriches and penguins

7. Mammalia (mammals):

Mammary glands for nursing young with milk

Hair or fur covering the body

Three middle ear bones

Diaphragm for breathing

Four-chambered heart

Viviparous (most species) or oviparous

Terrestrial, aerial, and aquatic habitats

Includes monotremes, marsupials, and placental mammals such as rodents, primates, carnivores, and whales.

Classification Of Animal Kingdom : FAQs

Q1. What is animal classification?

Ans. Animal classification is organising animals into groups based on their characteristics and evolutionary relationships. The classification system used by scientists is called taxonomy, and it involves arranging animals into different hierarchical levels, such as kingdom, phylum, class, order, family, genus, and species.

Q2. What is the basis of animal classification?

Ans. The basis of animal classification is their physical and genetic characteristics, behaviour, and evolutionary history. Scientists use various features to classify animals, such as body structure, internal organs, cell structure, DNA sequencing, and developmental processes.

Q3. What are the major animal phyla?

Ans. There are around 35 animal phyla. Still, the major ones include Porifera (sponges), Cnidaria (jellyfish, corals, anemones), Platyhelminthes (flatworms), Nematoda (roundworms), Annelida (segmented worms), Mollusca (snails, clams, squid), Arthropoda (insects, spiders, crustaceans), Echinodermata (starfish, sea urchins), and Chordata (vertebrates and their relatives).

Q4. What are the five kingdoms of living organisms?

Ans. The five kingdoms of living organisms are Monera (bacteria and cyanobacteria), Protista (single-celled eukaryotes), Fungi (yeasts, moulds, mushrooms), Plantae (plants), and Animalia (animals).