HSSLIVE Plus One Zoology Chapter 2: Animal Kingdom Notes – Hsslive | Hsslive.co.in | Hss Live

The animal kingdom represents one of the most diverse groups of organisms, with millions of species exhibiting remarkable adaptations. This chapter examines the classification of animals into various phyla based on body symmetry, tissue organization, body cavity, and developmental patterns. It highlights major animal groups from simple invertebrates like sponges and cnidarians to complex vertebrates, emphasizing evolutionary relationships and distinctive adaptations that have allowed animals to thrive in virtually every habitat on Earth.

Chapter 2: Animal Kingdom

Basis of Classification

Animals are classified based on several characteristics:

Levels of Organization: Cellular, tissue, organ, organ system
Symmetry: Asymmetrical, radial, bilateral
Germ Layers: Diploblastic (two layers), triploblastic (three layers)
Body Cavity (Coelom): Acoelomate, pseudocoelomate, coelomate
Segmentation: Presence or absence of body segments
Notochord: Presence or absence of this embryonic supporting structure

Classification of Animal Kingdom

NON-CHORDATA (Animals without notochord)

1. Phylum Porifera (Sponges)

Characteristics: Multicellular, pore-bearing, aquatic animals
Organization: Cellular level
Symmetry: Mostly asymmetrical
Skeleton: Made of spicules or spongin fibers
Canal System: For water circulation and food capturing
Examples: Bath sponge (Spongia), Sycon, Euplectella

2. Phylum Cnidaria (Coelenterata)

Characteristics: Aquatic, mostly marine animals
Organization: Tissue level
Symmetry: Radial
Body Wall: Diploblastic (ectoderm and endoderm)
Body Forms: Polyp (sessile) and Medusa (free-swimming)
Special Feature: Cnidoblasts/Nematocysts (stinging cells)
Examples: Hydra, jellyfish, sea anemone, corals

3. Phylum Platyhelminthes (Flatworms)

Characteristics: Dorsoventrally flattened bodies
Organization: Organ level
Symmetry: Bilateral
Body Wall: Triploblastic (ectoderm, mesoderm, endoderm)
Body Cavity: Acoelomate (no body cavity)
Digestive System: Incomplete (no anus)
Examples: Planaria, liver fluke, tapeworm

4. Phylum Nematoda (Roundworms)

Characteristics: Cylindrical, unsegmented worms
Organization: Organ-system level
Symmetry: Bilateral
Body Wall: Triploblastic
Body Cavity: Pseudocoelomate (false body cavity)
Digestive System: Complete (mouth to anus)
Examples: Ascaris, hookworm, pinworm

5. Phylum Annelida (Segmented worms)

Characteristics: Segmented body (metameres)
Organization: Organ-system level
Symmetry: Bilateral
Body Wall: Triploblastic
Body Cavity: Coelomate (true body cavity)
Special Features: Setae for locomotion, well-developed nervous system
Examples: Earthworm, leech, Nereis

6. Phylum Arthropoda (Joint-legged animals)

Characteristics: Largest phylum, jointed appendages
Organization: Organ-system level
Symmetry: Bilateral
Body Wall: Triploblastic
Body Cavity: Coelomate
Special Features: Exoskeleton of chitin, segmented body, open circulatory system
Examples: Insects, spiders, crustaceans, centipedes

7. Phylum Mollusca

Characteristics: Soft-bodied animals, often with shells
Organization: Organ-system level
Symmetry: Bilateral (most)
Body Wall: Triploblastic
Body Cavity: Coelomate
Special Features: Muscular foot, mantle, radula
Examples: Snails, clams, octopus, squid

8. Phylum Echinodermata

Characteristics: Marine animals with spiny skin
Organization: Organ-system level
Symmetry: Radial (adults); bilateral (larvae)
Body Wall: Triploblastic
Body Cavity: Coelomate
Special Features: Water vascular system, endoskeleton of calcareous plates
Examples: Starfish, sea urchin, sea cucumber

CHORDATA (Animals with notochord)

Characteristic Features:

Presence of notochord (at least during embryonic stage)
Dorsal hollow nerve cord
Pharyngeal gill slits (at some stage of life)
Post-anal tail

Subphylum Protochordata

Simple chordates without vertebral column
Examples: Amphioxus (lancelet), Herdmania (sea squirt)

Subphylum Vertebrata

Animals with vertebral column replacing notochord in adults.

Class Cyclostomata

Characteristics: Jawless fishes
Examples: Lampreys, hagfishes

Class Pisces (Fishes)

Characteristics: Aquatic, streamlined body, gills, fins
Subgroups: Cartilaginous fishes (sharks, rays) and Bony fishes (tuna, rohu)

Class Amphibia

Characteristics: Can live on land and water, moist skin, no scales
Examples: Frogs, toads, salamanders

Class Reptilia

Characteristics: Terrestrial, dry scaly skin, amniotic eggs
Examples: Lizards, snakes, turtles, crocodiles

Class Aves (Birds)

Characteristics: Feathers, forelimbs modified as wings, endothermic
Examples: Sparrow, pigeon, eagle

Class Mammalia

Characteristics: Hair, mammary glands, viviparity (mostly)
Examples: Humans, lions, whales, bats

Complete Chapter-wise Hsslive Plus One Zoology Notes

Our HSSLive Plus One Zoology Notes cover all chapters with key focus areas to help you organize your study effectively: