Animal Kingdom Classification

Kingdom Animalia

  • All animals are multicellular and heterotrophic.

  • Two major divisions based on vertebral column:

    • Invertebrates (lack a vertebral column).

    • Vertebrates (possess a vertebral column).

Invertebrates

  • There are 5 main phyla:

    1. Cnidaria / Coelenterata

    2. Annelida

    3. Mollusca

    4. Arthropoda

    5. Echinodermata

Phylum Cnidaria / Coelenterata

  • Examples: Hydra, Sea anemone, Coral polyp.

  • Key features:

    • Multicellular, 2 germ layers (diploblastic).

    • Central digestive cavity – coelenteron.

    • Two body forms: Medusa (free-swimming) & Polyp (sessile).

    • Radial symmetry.

    • Predatory; tentacles with nematoblasts (stinging cells) to paralyse prey.

  • Ecological note: Coral polyps build coral reefs, critical habitats for marine biodiversity.

Phylum Annelida

  • Examples: Earthworm, Leech, Nereis.

  • Features:

    • Triploblastic (three germ layers).

    • True coelom \rightarrow independent gut movement.

    • Body segmented internally & externally (“segmented worms”).

    • Bilateral symmetry; elongated cylindrical form.

    • May reproduce sexually or asexually.

    • Distinct structures: setae, clitellum, fertilised eggs visible in cocoons.

    • Habitats: terrestrial, freshwater, marine.

Phylum Mollusca

  • Examples: Snail, Slug, Oyster, Octopus, Squid.

  • Second-largest phylum by species count (after Arthropoda).

  • Features:

    • Soft-bodied; unsegmented.

    • Body parts: muscular foot, visceral mass, mantle (often secretes CaCO_3 shell).

    • Body kept moist with mucus.

    • Bilateral symmetry.

    • Mostly unisexual; sexual reproduction predominates.

    • Habitats largely marine, also freshwater & terrestrial.

Phylum Arthropoda

  • Largest phylum; about 75\% of all animal species.

    • Class Insecta is the most speciose subgroup.

  • Examples pictured: Insects, Barnacle, Spider, Scorpion, Centipede.

  • Features:

    • Triploblastic, coelomic, segmented.

    • Jointed appendages ("arthro" = joint, "podos" = foot).

    • Segments fuse into functional tagmata: head, thorax, abdomen.

    • External chitinous cuticle forms an exoskeleton; may bear wings.

    • Distinct sexes; sexual dimorphism common.

    • Terrestrial, aerial, freshwater, marine habitats.

  • Activity suggestion: create an insect display box from household specimens.

Phylum Echinodermata

  • Examples: Sea urchin, Sea cucumber, Starfish (implied).

  • Evolutionarily close to chordates.

  • Features:

    • Exclusively marine.

    • Triploblastic, coelomic.

    • Adults show penta-radial symmetry; body in 5 arms.

    • Spiny endoskeleton just beneath the skin.

    • Unique water-vascular system with tube feet for movement, gas exchange, excretion.

    • Separate sexes; sexual reproduction.

Vertebrates (Phylum Chordata) – Common Diagnoses

At some stage of life every vertebrate exhibits:

  • \textit{Notochord}

  • Hollow dorsal \textit{spinal chord}

  • Pharyngeal \textit{gill slits}

  • Muscular \textit{post-anal tail}

  • Ventral, chambered heart

Five major classes:

  1. Pisces

  2. Amphibia

  3. Reptilia

  4. Aves

  5. Mammalia

Class Pisces (Fish)

  • Fully aquatic (freshwater & marine).

  • Streamlined body with scales.

  • Endoskeleton of bone or cartilage.

  • Paired fins; lateral line for vibration detection.

  • Cold-blooded (poikilothermic).

  • Two-chambered heart: 1 atrium + 1 ventricle.

  • Eyes without eyelids.

Subclass Comparison

Characteristic

Chondrichthyes (Cartilaginous)

Osteichthyes (Bony)

Skeleton

Cartilage

Bone

Swim bladder

Absent

Present

Mouth position

Ventral

Terminal

Scales

Placoid

Cycloid / Ctenoid

Gill cover (operculum)

Absent – gill slits exposed

Present – gills hidden

Examples

Shark, Skate

Rohu, Tuna, Sea horse

Class Amphibia

  • Dual life: water (larval) & land (adult).

  • Examples: Frog, Toad, Salamander, Caecilian (Ichthyophis).

  • Moist glandular skin, no scales.

  • Pentadactyl limbs for locomotion.

  • Three-chambered heart ( 2 atria + 1 ventricle ).

  • Gas exchange via gills, lungs, and/or skin.

  • Cold-blooded.

Class Reptilia

  • Terrestrial adaptations.

  • Examples: Tortoise, Crocodile, Lizard, Cobra.

  • Dry, glandless skin with keratinised scales.

  • Pentadactyl limbs (limbless in snakes).

  • Heart: 2 atria + incompletely divided ventricle (crocodiles have 4 chambers).

  • Lungs used exclusively for respiration.

  • Internal fertilisation; amniotic eggs with leathery shells.

  • Cold-blooded.

Class Aves (Birds)

  • Examples: Ostrich (largest), Penguin (flightless swimmer).

  • Lightweight bony endoskeleton with air sacs; forelimbs modified to wings.

  • Body covered by feathers; scales only on legs.

  • Toothless beak specialised for feeding mode.

  • Eyes with eyelids; keen vision.

  • Four-chambered heart with complete double circulation.

  • Efficient lungs plus air sacs for continuous airflow.

  • Warm-blooded (homeothermic).

  • Internal fertilisation; hard-shelled eggs; parental care common.

Class Mammalia

  • Examples/illustrations: Bat (only flying mammal), Dolphin (aquatic), Human, Elephant.

  • Diagnostic traits:

    • Hair (in follicles) covering skin.

    • Mammary glands producing milk for young.

    • External ear lobes (pinnae).

    • Four-chambered heart with complete double circulation.

    • Enucleated, biconcave RBCs.

    • Diaphragm separates thorax & abdomen.

    • Testes in scrotal sac (except some exceptions).

    • Internal fertilisation, placenta, embryonic membranes.

    • Warm-blooded.

  • Selected orders (for extra insight):

    1. Primates – Shrew, Loris, Monkey, Orangutan, Gorilla, Chimpanzee, Human.

    2. Chiroptera – Bat.

    3. Cetacea – Whale, Dolphin.

    4. Artiodactyla – Cow, Deer, Giraffe, etc.

Scientific Naming – Binomial Nomenclature

  • Introduced by Swiss naturalist Carolus Linnaeus.

  • Governed by:

    • International Code of Botanical Nomenclature (ICBN).

    • International Code of Zoological Nomenclature (ICZN).

  • Key conventions:

    • Each species name = Genus name + specific epithet.

    • Printed in italics; Genus capitalised, specific epithet lower-case.

    • Universal, avoids local language confusion.

  • Examples:

    • Man – Homo sapiens.

    • Asian Elephant – Elephas maximus.

    • Junglefowl – Gallus lafayetti.

    • Asoka pethiya (fish) – Puntius asoka.

    • Blue water-lily – Nymphaea stellata.

    • Ceylon ironwood (Na) – Mesua nagassarium.

    • Coconut – Cocos nucifera.

Ethical, Ecological & Practical Notes

  • Coral reefs (Cnidaria) underpin marine food webs; their destruction threatens fishery & tourism industries.

  • Arthropods’ dominance ( > 1 million species) implies huge ecological services (pollination, decomposition) and pest potentials.

  • Insect collection boxes aid student familiarity but should follow ethical guidelines (use already dead specimens).

  • Reptile and bird egg structures (amniotic egg, hard shell) represent crucial terrestrial adaptations inspiring biomimetic materials science.

  • Mammalian placenta research has medical relevance for human pregnancy and neonatal care.

Quick Comparative Heart Chambers

Class

Chambers

Thermal Strategy

Pisces

2

Cold-blooded

Amphibia

3

Cold-blooded

Reptilia

3 (incomplete 4)

Cold-blooded

Aves

4

Warm-blooded

Mammalia

4

Warm-blooded

Memory Aids & Connections

  • Radial \rightarrow Cnidaria ( 2 layers ) & adult Echinodermata ( 5-part).

  • "Seg-mented" \rightarrow Annelida (external & internal) vs. Arthropoda (external exoskeleton + jointed appendages).

  • "Moist skin" \rightarrow Amphibia; "Dry scales" \rightarrow Reptilia; "Feathers" \rightarrow Aves; "Hair + milk" \rightarrow Mammalia.