Animal Kingdom
Explore the amazing diversity of animal life and understand the fundamental principles of animal classification in this comprehensive chapter.
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Brief Introduction
The animal kingdom exhibits an enormous diversity in form and structure. With over a million species described, classification becomes essential for systematic study. This chapter introduces the fundamental features used in animal classification and explores the major phyla of the animal kingdom.
Learning Objectives
- Understand the basis of animal classification
- Learn about levels of organization and body symmetry
- Study diploblastic and triploblastic organization
- Comprehend coelom formation and types
- Explore the classification of animals into different phyla
- Understand the distinctive features of chordates
Key Topics Covered
- Basis of Classification
- Levels of Organization
- Body Symmetry
- Germinal Layers
- Coelom Types
- Phylum Porifera to Chordata
- Vertebrate Classification
- Comparative Study of Animal Phyla
Interactive Chapter Index
Basis of Classification
Explore the fundamental features used to classify animals including organization, symmetry, and germ layers.
Phylum Porifera
Learn about the simplest multicellular animals - the sponges with cellular level organization.
Phylum Coelenterata
Study the radially symmetrical, diploblastic animals with tissue level organization.
Phylum Platyhelminthes
Discover the flatworms - bilaterally symmetrical, triploblastic, acoelomate animals.
Phylum Annelida
Explore the segmented worms with true coelom and organ-system level organization.
Phylum Chordata
Understand the animals with notochord, dorsal nerve cord and pharyngeal gill slits.
Full Chapter Notes
4.1 Basis of Classification
Despite differences in structure and form among animals, there are fundamental features common to various individuals in relation to the arrangement of cells, body symmetry, nature of coelom, patterns of digestive, circulatory or reproductive systems. These features are used as the basis of animal classification.
4.1.1 Levels of Organisation
- Cellular level: Cells arranged as loose aggregates (e.g., sponges)
- Tissue level: Cells performing same function arranged into tissues (e.g., coelenterates)
- Organ level: Tissues grouped together to form organs (e.g., Platyhelminthes)
- Organ system level: Organs associated to form functional systems (e.g., Annelids, Arthropods, Chordates)
4.1.2 Symmetry
- Asymmetrical: No symmetry (e.g., sponges)
- Radial symmetry: Any plane passing through central axis divides into identical halves (e.g., coelenterates, echinoderms)
- Bilateral symmetry: Body can be divided into identical left and right halves in only one plane (e.g., annelids, arthropods)
4.1.3 Diploblastic and Triploblastic Organisation
- Diploblastic: Cells arranged in two embryonic layers (ectoderm and endoderm) with mesoglea in between (e.g., coelenterates)
- Triploblastic: Developing embryo has three germinal layers (ectoderm, mesoderm, endoderm) (e.g., platyhelminthes to chordates)
4.1.4 Coelom
- Coelomates: Have true coelom lined by mesoderm (e.g., annelids, chordates)
- Pseudocoelomates: Body cavity not lined by mesoderm (e.g., aschelminthes)
- Acoelomates: No body cavity (e.g., platyhelminthes)
4.1.5 Segmentation
In some animals, the body is externally and internally divided into segments with a serial repetition of at least some organs (e.g., earthworm shows metameric segmentation).
4.1.6 Notochord
- Chordates: Animals with notochord (a mesodermally derived rod-like structure)
- Non-chordates: Animals without notochord (e.g., porifera to echinoderms)
4.2.1 Phylum – Porifera
Commonly known as sponges, these are generally marine and mostly asymmetrical animals with cellular level of organization.
Key Features:
- Primitive multicellular animals
- Have water transport or canal system
- Body supported by skeleton made of spicules or spongin fibers
- Digestion is intracellular
- Reproduce asexually by fragmentation and sexually by gametes
- Hermaphrodite (sexes not separate)
4.2.2 Phylum – Coelenterata (Cnidaria)
Aquatic, mostly marine, sessile or free-swimming, radially symmetrical animals with tissue level of organization.
Key Features:
- Have cnidoblasts or cnidocytes (stinging cells) for defense and prey capture
- Diploblastic with tissue level organization
- Central gastro-vascular cavity with single opening
- Exhibit two basic body forms: polyp (sessile) and medusa (free-swimming)
- Some show alternation of generation (metagenesis)
4.2.4 Phylum – Platyhelminthes
Flatworms with dorso-ventrally flattened body, mostly endoparasites with organ level of organization.
Key Features:
- Bilaterally symmetrical, triploblastic, acoelomate
- Parasitic forms have hooks and suckers
- Flame cells help in osmoregulation and excretion
- Hermaphrodite (sexes not separate)
- High regeneration capacity (e.g., Planaria)
4.2.6 Phylum – Annelida
Segmented worms (metamerically segmented) with true coelom and organ-system level of organization.
Key Features:
- Bilaterally symmetrical, triploblastic, coelomate
- Body divided into segments (metameres)
- Have longitudinal and circular muscles for locomotion
- Closed circulatory system
- Nephridia help in osmoregulation and excretion
- May be monoecious or dioecious
4.2.11 Phylum – Chordata
Animals characterized by the presence of notochord, dorsal hollow nerve cord and paired pharyngeal gill slits at some stage of their life.
Key Features:
- Bilaterally symmetrical, triploblastic, coelomate
- Organ-system level of organization
- Possess notochord, dorsal nerve cord, pharyngeal gill slits
- Have post-anal tail and closed circulatory system
Subphyla of Chordata:
- Urochordata: Notochord only in larval tail (e.g., Ascidia)
- Cephalochordata: Notochord extends from head to tail (e.g., Branchiostoma)
- Vertebrata: Notochord replaced by vertebral column in adults
Classification of Vertebrates:
| Class | Characteristics | Examples |
|---|---|---|
| Cyclostomata | Jawless, eel-like, ectoparasites on fishes | Lamprey, Hagfish |
| Chondrichthyes | Cartilaginous fishes, streamlined body | Shark, Ray |
| Osteichthyes | Bony fishes, operculum present | Rohu, Sea horse |
| Amphibia | Live in water and on land, moist skin | Frog, Toad |
| Reptilia | Dry scaly skin, cold-blooded | Snake, Lizard |
| Aves | Feathers, beak, wings, warm-blooded | Pigeon, Ostrich |
| Mammalia | Mammary glands, hair, warm-blooded | Human, Whale |
Comparative Study of Animal Phyla
| Phylum | Level of Organisation | Symmetry | Coelom | Digestive System | Distinctive Features |
|---|---|---|---|---|---|
| Porifera | Cellular | Asymmetrical | Absent | Absent | Pores and canals in walls |
| Coelenterata | Tissue | Radial | Absent | Incomplete | Cnidoblasts present |
| Platyhelminthes | Organ-system | Bilateral | Absent | Incomplete | Flat body, suckers |
| Annelida | Organ-system | Bilateral | Coelomate | Complete | Body segmentation |
| Arthropoda | Organ-system | Bilateral | Coelomate | Complete | Jointed appendages |
| Chordata | Organ-system | Bilateral | Coelomate | Complete | Notochord present |
Chapter Summary
Key Takeaways:
- Animals are classified based on fundamental features like organization, symmetry, germ layers, coelom, segmentation and notochord
- Porifera are the simplest multicellular animals with cellular level organization
- Coelenterata are diploblastic with radial symmetry and cnidoblasts
- Platyhelminthes are flatworms with organ level organization
- Annelids are segmented worms with true coelom
- Arthropods are the largest phylum with jointed appendages
- Chordates are characterized by notochord, dorsal nerve cord and pharyngeal gill slits
- Vertebrates have vertebral column replacing notochord in adults
NCERT Solutions
Question 1: What are the difficulties that you would face in classification of animals, if common fundamental features are not taken into account?
Without considering common fundamental features, classification would face these difficulties:
- No standardized basis for grouping organisms
- Difficulty in establishing evolutionary relationships
- Inconsistent classification systems
- Hard to identify newly discovered species
- No framework to compare different groups
- Chaotic and arbitrary classification
Question 2: If you are given a specimen, what are the steps that you would follow to classify it?
Steps to classify a specimen:
- Observe external morphology (shape, size, symmetry)
- Study internal anatomy (dissection if needed)
- Note cellular organization (tissues, organs)
- Check for presence of coelom
- Identify germ layers (diploblastic/triploblastic)
- Look for specialized structures (notochord, appendages)
- Compare with known classification systems
- Assign to appropriate phylum and class
Question 3: How useful is the study of the nature of body cavity and coelom in the classification of animals?
Study of body cavity and coelom is very useful because:
- Helps divide animals into three main groups: acoelomates, pseudocoelomates, coelomates
- Reflects complexity of body organization
- Indicates evolutionary advancement
- Correlates with development of organ systems
- Provides important taxonomic character
Question 4: Distinguish between intracellular and extracellular digestion?
| Feature | Intracellular Digestion | Extracellular Digestion |
|---|---|---|
| Location | Inside cells | Outside cells (in cavities) |
| Complexity | Primitive | Advanced |
| Examples | Porifera, some protozoans | Most animals from coelenterates onwards |
| Efficiency | Limited to small food particles | Can handle larger food items |
Question 5: What is the difference between direct and indirect development?
| Feature | Direct Development | Indirect Development |
|---|---|---|
| Definition | Young resembles adult | Young differs from adult (larval stage) |
| Metamorphosis | Absent | Present |
| Examples | Humans, birds | Frogs, insects |
| Advantage | No vulnerable larval stage | Larvae and adults occupy different niches |
Question 6: What are the peculiar features that you find in parasitic platyhelminthes?
Peculiar features of parasitic flatworms:
- Flattened body for increased surface area
- Presence of hooks and suckers for attachment
- Thick tegument resistant to host enzymes
- Reduced digestive system (absorb nutrients directly)
- Complex life cycles with intermediate hosts
- High reproductive capacity (many eggs)
- Anaerobic respiration in some intestinal parasites
Question 7: What are the reasons that you can think of for the arthropods to constitute the largest group of the animal kingdom?
Reasons for arthropod dominance:
- Exoskeleton provides protection and support
- Jointed appendages allow diverse locomotion
- High adaptability to various habitats
- Small size requires less resources
- High reproductive potential
- Efficient respiratory systems (trachea, gills)
- Well-developed sensory organs
- Diverse feeding habits
Question 8: Water vascular system is the characteristic of which group of the following: (a) Porifera (b) Ctenophora (c) Echinodermata (d) Chordata
Correct Answer: (c) Echinodermata
The water vascular system is a unique feature of echinoderms (starfish, sea urchins) used for locomotion, food capture and respiration.
Question 10: How important is the presence of air bladder in Pisces?
The air bladder (swim bladder) is very important for bony fishes because:
- Helps in buoyancy control (maintain position in water)
- Reduces energy expenditure for swimming
- In some species, aids in respiration
- May function as sound producer or receptor
- Absent in cartilaginous fishes which must swim constantly
Question 11: What are the modifications that are observed in birds that help them fly?
Flight adaptations in birds:
- Forelimbs modified into wings
- Lightweight body with pneumatic bones
- Streamlined body shape
- Feathers for flight and insulation
- Powerful flight muscles
- Efficient respiratory system with air sacs
- Reduced body weight (no urinary bladder, single ovary)
- Beak instead of heavy jaws
Question 13: Segmentation in the body is first observed in which of the following: (a) Platyhelminthes (b) Aschelminthes (c) Annelida (d) Arthropoda
Correct Answer: (c) Annelida
Annelids are the first phylum to show true metameric segmentation where the body is divided into similar segments both externally and internally.
Question 14: Match the following:
| Column A | Column B |
|---|---|
| (a) Operculum | (viii) Osteichthyes |
| (b) Parapodia | (v) Annelida |
| (c) Scales | (iv) Reptilia |
| (d) Comb plates | (i) Ctenophora |
| (e) Radula | (ii) Mollusca |
| (f) Hairs | (vii) Mammalia |
| (g) Choanocytes | (iii) Porifera |
| (h) Gill slits | (vi) Cyclostomata and Chondrichthyes |
Question 15: Prepare a list of some animals that are found parasitic on human beings.
Animals parasitic on humans:
- Protozoans: Entamoeba histolytica, Plasmodium (malaria parasite), Giardia
- Flatworms: Taenia solium (tapeworm), Fasciola hepatica (liver fluke)
- Roundworms: Ascaris, Wuchereria (filaria), Ancylostoma (hookworm)
- Arthropods: Lice, fleas, ticks, mites
- Annelids: Leeches
Practice Questions
Correct Answer: d) Ventral solid nerve cord
Explanation: Chordates are characterized by dorsal hollow nerve cord, not ventral solid nerve cord which is found in non-chordates.
Correct Answer: b) Coelenterata
Explanation: Cnidoblasts or cnidocytes are stinging cells characteristic of phylum Coelenterata (Cnidaria).
Correct Answer: d) Platyhelminthes - Bilateral
Explanation: Platyhelminthes are bilaterally symmetrical. Coelenterates are radially symmetrical, annelids are bilaterally symmetrical, and adult echinoderms are radially symmetrical (though larvae are bilateral).
Answer:
| Feature | Diploblastic | Triploblastic |
|---|---|---|
| Germ Layers | Two (ectoderm and endoderm) | Three (ectoderm, mesoderm, endoderm) |
| Mesoglea | Present | Absent |
| Complexity | Simpler | More complex |
| Examples | Coelenterates | Platyhelminthes to Chordates |
Answer: Distinctive features of Arthropoda:
- Jointed appendages (arthros-joint, poda-appendages)
- Body covered by chitinous exoskeleton
- Body divided into head, thorax and abdomen
- Open circulatory system
- Respiratory organs vary (gills, book lungs, trachea)
- Excretion through malpighian tubules
- Well-developed sensory organs
- Mostly dioecious
Answer:
Basis of animal classification:
- Levels of organization: Cellular, tissue, organ, organ-system
- Symmetry: Asymmetrical, radial, bilateral
- Germ layers: Diploblastic, triploblastic
- Coelom: Acoelomate, pseudocoelomate, coelomate
- Segmentation: Presence or absence of metamerism
- Notochord: Presence or absence
- Other features: Digestive system, circulatory system, reproductive patterns
Helps in understanding evolutionary relationships by:
- Showing progression from simple to complex organization
- Revealing common ancestry through shared characteristics
- Demonstrating adaptive radiation in different environments
- Highlighting key evolutionary innovations (e.g., coelom, segmentation)
- Providing framework to trace lineage and divergence
Answer:
| Feature | Chordates | Non-chordates |
|---|---|---|
| Notochord | Present at some stage | Absent |
| Nerve cord | Dorsal, hollow | Ventral, solid |
| Gill slits | Present at some stage | Absent |
| Heart | Ventral | Dorsal (if present) |
| Post-anal tail | Present at some stage | Absent |
| Blood vascular system | Closed | Open (usually) |
Interactive Flashcards
What are the three germ layers in triploblastic animals?
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The three germ layers are:
- Ectoderm (outer layer)
- Mesoderm (middle layer)
- Endoderm (inner layer)
These give rise to all tissues and organs in the body.
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