Kingdom Animalia

 Summary

Animals are multicellular eukaryotes with specialized tissues and organ systems. They reproduce mainly sexually, show mobility at some stage of life, and respond actively to environmental changes.

• Nutrition: Heterotrophic — depend on plants or other animals.
• Cell structure: No cell wall; contain centrioles.
• Reproduction: Mostly sexual, with distinct male and female gametes.
• Habitat: Found everywhere — land, water, and air.
• Importance: Maintain ecological balance, provide food, clothing, and companionship.

Keywords

Animalia, Heterotrophic, Invertebrates, Vertebrates, Multicellular, Eukaryotic.

Kingdom Animalia

Kingdom Animalia, also known as the animal kingdom, includes all multicellular, eukaryotic, and heterotrophic organisms that depend on other living things for food. Animals form a vital part of ecosystems — from microscopic invertebrates to large vertebrates — each playing a unique ecological role.

Unlike plants, animals lack cell walls and do not perform photosynthesis. Instead, they ingest, digest, and metabolize food internally for energy and growth.

Characteristics of Kingdom Animalia

1. Cell Structure

• Eukaryotic cells with nucleus and organelles.
• No cell wall (unlike plants or fungi).
• Cells are organized into tissues, organs, and systems.

2. Mode of Nutrition

• Heterotrophic: Animals cannot make their own food.
• Obtain nutrients by ingestion and digestion.
• Based on diet:
• Herbivores: Eat plants (e.g., Cow, Deer).
• Carnivores: Eat other animals (e.g., Lion, Tiger).
• Omnivores: Eat both (e.g., Humans, Bears).

3. Body Organization

• Multicellular with increasing complexity — from sponges to humans.
• Most animals have symmetry:
• Radial symmetry: e.g., Starfish.
• Bilateral symmetry: e.g., Humans, Dogs.

4. Movement

• Most animals show voluntary movement using muscles.
• Locomotion includes walking, flying, swimming, or crawling.

5. Reproduction

• Sexual reproduction is common (fusion of sperm and egg).
• Some also reproduce asexually (budding, fragmentation, parthenogenesis).
• Embryonic development includes zygote → embryo → adult stages.

6. Nervous and Sensory System

• Most animals have well-developed nervous systems.
• Sense organs detect light, sound, taste, and touch, allowing quick responses to stimuli.

Classification of Kingdom Animalia

Scientists divide animals into two main groups:
1. Invertebrates (no backbone)
2. Vertebrates (with backbone)

1. Invertebrates

Invertebrates make up nearly 95% of all animal species. They lack a vertebral column (backbone) and are often small or soft-bodied.

Major Phyla of Invertebrates:

1.     Porifera (Sponges)

o    Simplest multicellular animals.

o    Body has pores for water flow.

o    Example: Sycon, Spongilla.

2.     Coelenterata / Cnidaria (Jellyfish, Corals)

o    Have stinging cells called cnidocytes.

o    Radial symmetry.

o    Example: Hydra, Aurelia (Jellyfish).

3.     Platyhelminthes (Flatworms)

o    Flattened, soft bodies; many are parasites.

o    Example: Tapeworm, Planaria.

4.     Nematoda (Roundworms)

o    Cylindrical, unsegmented worms; some cause diseases.

o    Example: Ascaris (Roundworm).

5.     Annelida (Segmented Worms)

o    Body divided into ring-like segments.

o    Have a true body cavity.

o    Example: Earthworm, Leech.

6.     Arthropoda (Insects, Crustaceans, Arachnids)

o    Most diverse phylum; jointed legs and exoskeleton.

o    Examples: Butterfly, Crab, Spider.

7.     Mollusca (Soft-bodied animals)

o    Have soft bodies, often protected by shells.

o    Examples: Snail, Octopus, Mussel.

8.     Echinodermata (Spiny-skinned animals)

o    Marine animals with radial symmetry.

o    Examples: Starfish, Sea urchin.

2. Vertebrates (Chordates)

Vertebrates have a notochord or backbone that supports the body and protects the spinal cord.

Major Groups of Vertebrates:

1.     Pisces (Fishes)

o    Aquatic, cold-blooded, breathe through gills.

o    Examples: Rohu, Shark, Goldfish.

2.     Amphibia (Frogs, Salamanders)

o    Live on land and water; breathe through lungs and skin.

o    Examples: Frog, Toad.

3.     Reptilia (Reptiles)

o    Dry skin with scales; lay eggs on land.

o    Examples: Snake, Lizard, Crocodile.

4.     Aves (Birds)

o    Warm-blooded, feathers, lay eggs, can fly (mostly).

o    Examples: Sparrow, Eagle, Parrot.

5.     Mammalia (Mammals)

o    Have hair/fur, produce milk for young, warm-blooded.

o    Examples: Human, Cow, Whale, Bat.

Significance of Kingdom Animalia

1. Ecological Balance

Animals maintain the food chain and regulate population dynamics in ecosystems.

2. Food Source

Provide meat, milk, eggs, honey, and seafood — essential protein sources for humans.

3. Agriculture & Industry

Animals like oxen and horses assist in farming. Silkworms, bees, and sheep provide silk, honey, and wool.

4. Companionship & Research

Pets like dogs and cats offer companionship; lab animals aid in medical and biological research.

5. Environmental Indicators

Certain species (like frogs) act as bio-indicators, showing ecosystem health.

Conclusion

Kingdom Animalia represents the most diverse and dynamic life forms on Earth. From microscopic creatures to massive mammals, animals play crucial roles in sustaining life, shaping ecosystems, and supporting human civilization. Understanding their classification and behavior deepens our appreciation for the balance of nature.