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Solve each Samacheer Kalvi exercise question on your own first, then compare your answer with the solutions below. Kingdom Animalia covers the basis of animal classification and key features of each phylum — focus on understanding the distinguishing characteristics.
Key Concepts (Quick Recap)
Basis of Animal Classification
| Feature | Types | Examples |
|---|
| Symmetry | Asymmetrical, Radial, Bilateral | Sponges, Jellyfish, Most animals |
| Germ layers | Diploblastic (2), Triploblastic (3) | Cnidaria, Platyhelminthes onwards |
| Coelom | Acoelomate, Pseudocoelomate, Coelomate | Flatworms, Roundworms, Annelids |
| Segmentation | Unsegmented, Segmented | Platyhelminthes, Annelida/Arthropoda |
| Notochord | Present (Chordata), Absent (Non-chordata) | Vertebrates, Invertebrates |
Phyla of Kingdom Animalia — Key Features
| Phylum | Symmetry | Coelom | Key Features | Examples |
|---|
| Porifera | Asymmetrical/irregular | No coelom | Pores (ostia), canal system, spicules | Sycon, Spongilla, Euspongia |
| Cnidaria | Radial | No coelom | Cnidoblasts (stinging cells), tentacles, gastrovascular cavity | Hydra, Jellyfish, Sea anemone, Corals |
| Platyhelminthes | Bilateral | Acoelomate | Flat body, flame cells, hermaphrodite | Planaria, Liver fluke, Tapeworm |
| Aschelminthes | Bilateral | Pseudocoelomate | Round body, unsegmented, separate sexes | Ascaris (roundworm), Wuchereria (filaria) |
| Annelida | Bilateral | Coelomate | Metameric segmentation, nephridia, closed circulation | Earthworm, Leech, Nereis |
| Arthropoda | Bilateral | Coelomate | Exoskeleton (chitin), jointed appendages, haemocoel | Cockroach, Butterfly, Spider, Crab |
| Mollusca | Bilateral | Coelomate (reduced) | Shell, mantle, muscular foot, radula | Snail, Octopus, Pila, Pearl oyster |
| Echinodermata | Radial (pentamerous) | Coelomate | Water vascular system, tube feet, spiny skin | Starfish, Sea urchin, Sea cucumber |
| Chordata | Bilateral | Coelomate | Notochord, dorsal nerve cord, gill slits, post-anal tail | Fish, Frog, Bird, Human |
Coelom Types Explained
| Type | Description | Lined by Mesoderm | Examples |
|---|
| Acoelomate | No body cavity | No | Platyhelminthes (flatworms) |
| Pseudocoelomate | Body cavity partially lined by mesoderm | Partially | Aschelminthes (roundworms) |
| Coelomate | True body cavity fully lined by mesoderm | Fully | Annelida, Arthropoda, Mollusca, Chordata |
Chordata — Sub-phyla and Classes
| Group | Notochord | Examples |
|---|
| Hemichordata | Proboscis (partial notochord) | Balanoglossus |
| Urochordata | Only in larval tail | Ascidia, Salpa |
| Cephalochordata | Throughout life | Branchiostoma (Amphioxus) |
| Vertebrata | Replaced by vertebral column | Fish, Amphibians, Reptiles, Birds, Mammals |
Vertebrata — Classes
| Class | Heart | Respiration | Habitat | Examples |
|---|
| Pisces | 2-chambered | Gills | Aquatic | Shark, Rohu, Dogfish |
| Amphibia | 3-chambered | Lungs + skin | Dual | Frog, Toad, Salamander |
| Reptilia | 3-chambered (partially 4 in crocodile) | Lungs | Terrestrial | Snake, Lizard, Crocodile, Turtle |
| Aves | 4-chambered | Lungs | Aerial | Sparrow, Pigeon, Ostrich |
| Mammalia | 4-chambered | Lungs | All habitats | Human, Bat, Whale, Kangaroo |
I. Choose the Best Answer (MCQs)
Q1. Animals with radial symmetry are found in the phylum (a) Porifera (b) Platyhelminthes (c) Cnidaria (d) Annelida
Answer(c) Cnidaria — Cnidarians (jellyfish, sea anemones, corals) have radial symmetry where body parts are arranged around a central axis. Sponges (Porifera) are mostly asymmetrical. Platyhelminthes and Annelida have bilateral symmetry.
Q2. The phylum with jointed appendages and exoskeleton is (a) Mollusca (b) Annelida (c) Arthropoda (d) Echinodermata
Answer(c) Arthropoda — Arthropods are characterised by jointed appendages (arthro = jointed, pod = foot) and a hard exoskeleton made of chitin. They are the largest phylum in the animal kingdom.
Q3. Flame cells are the excretory organs of (a) Annelida (b) Platyhelminthes (c) Arthropoda (d) Mollusca
Answer(b) Platyhelminthes — Flame cells (solenocytes) are specialised excretory structures found in flatworms (Platyhelminthes). They help in osmoregulation and removing waste. Annelids have nephridia, Arthropods have Malpighian tubules.
Q4. Which of the following is a pseudocoelomate animal? (a) Earthworm (b) Planaria (c) Ascaris (d) Hydra
Answer(c) Ascaris — Ascaris (roundworm) belongs to phylum Aschelminthes which has a pseudocoelom — a body cavity that is not fully lined by mesoderm. Earthworm is coelomate (Annelida), Planaria is acoelomate (Platyhelminthes), Hydra has no coelom (Cnidaria).
Q5. The water vascular system is a characteristic feature of (a) Mollusca (b) Echinodermata (c) Arthropoda (d) Cnidaria
Answer(b) Echinodermata — Echinoderms (starfish, sea urchins) have a unique water vascular system that operates their tube feet for locomotion, respiration, and food capture.
Q6. The largest phylum in the animal kingdom is (a) Chordata (b) Mollusca (c) Arthropoda (d) Annelida
Answer(c) Arthropoda — Arthropoda is the largest phylum, containing about 80% of all animal species. It includes insects, spiders, crustaceans, and millipedes.
II. Fill in the Blanks
1. The phylum Porifera includes animals with pores (ostia) and a canal system. 2. Cnidarians have stinging cells called cnidoblasts (nematocysts). 3. Flatworms belong to the phylum Platyhelminthes. 4. Roundworms belong to the phylum Aschelminthes (Nematoda). 5. Earthworms belong to the phylum Annelida. 6. The largest phylum in the animal kingdom is Arthropoda. 7. Animals with no body cavity are called acoelomate. 8. Animals with a true body cavity fully lined by mesoderm are called coelomate. 9. The excretory organs of Annelida are nephridia. 10. The excretory organs of Arthropoda are Malpighian tubules. 11. Chordates possess a notochord, dorsal hollow nerve cord, and pharyngeal gill slits. 12. The water vascular system is found in Echinodermata.
III. True or False (with corrections for false statements)
Q1. Sponges have true tissues.
AnswerFalse — Correction: Sponges (Porifera) do NOT have true tissues. They have a cellular level of organisation where cells are loosely arranged and can reform if separated. They are the only multicellular animals without true tissues.
Q2. Cnidarians have both polyp and medusa forms.
AnswerTrue — Many cnidarians exhibit alternation of generations between the polyp (sessile, cylindrical) and medusa (free-swimming, umbrella-shaped) forms. Example: Obelia has both polyp and medusa stages.
Q3. Ascaris is a coelomate animal.
AnswerFalse — Correction: Ascaris is a pseudocoelomate animal (phylum Aschelminthes). It has a body cavity that is not fully lined by mesoderm. Coelomate animals have a true coelom fully lined by mesoderm.
Q4. Arthropods have an exoskeleton made of chitin.
AnswerTrue — Arthropods have a hard exoskeleton made of chitin (and sometimes calcium carbonate). This exoskeleton provides protection and support, but must be moulted (shed) periodically for growth.
Q5. All chordates are vertebrates.
AnswerFalse — Correction: All vertebrates are chordates, but NOT all chordates are vertebrates. Protochordates (Hemichordata, Urochordata, Cephalochordata) have a notochord but do not have a vertebral column. Only the sub-phylum Vertebrata has a vertebral column.
IV. Match the Following
| Column A | Column B | Answer |
|---|
| 1. Porifera | (a) Jointed appendages | (b) Pores and canal system |
| 2. Cnidaria | (b) Pores and canal system | (c) Cnidoblasts |
| 3. Platyhelminthes | (c) Cnidoblasts | (d) Flame cells |
| 4. Aschelminthes | (d) Flame cells | (e) Pseudocoelomate |
| 5. Annelida | (e) Pseudocoelomate | (f) Nephridia, segmented |
| 6. Arthropoda | (f) Nephridia, segmented | (a) Jointed appendages |
V. Answer Briefly (2-mark questions)
Q1. Distinguish between diploblastic and triploblastic animals.
Answer
| Feature | Diploblastic | Triploblastic | |---|---|---| | Germ layers | Two (ectoderm, endoderm) | Three (ectoderm, mesoderm, endoderm) | | Mesoderm | Absent | Present | | Body cavity | Absent | May be present (acoelomate, pseudocoelomate, coelomate) | | Examples | Cnidaria (Hydra, Jellyfish) | Platyhelminthes to Chordata |
Q2. What is the difference between acoelomate, pseudocoelomate, and coelomate?
Answer
| Type | Body cavity | Lined by mesoderm | Example | |---|---|---|---| | Acoelomate | No body cavity | No | Flatworms (Platyhelminthes) | | Pseudocoelomate | Partially lined cavity | Partially | Roundworms (Aschelminthes) | | Coelomate | True coelom (fully lined) | Fully | Annelida, Arthropoda, Chordata |
Q3. List the distinguishing features of phylum Arthropoda.
Answer
1. Jointed appendages (arthro = jointed, pod = foot) 2. Exoskeleton made of chitin (moulted periodically) 3. Segmented body (head, thorax, abdomen) 4. Open circulatory system (haemocoel) 5. Malpighian tubules for excretion (in insects) 6. Largest phylum — about 80% of all animal species 7. Examples: Cockroach, Butterfly, Spider, Crab, Millipede
Q4. What are the four defining features of chordates?
Answer
All chordates possess four key features at some stage of their life: 1. Notochord: A dorsal, flexible supporting rod (replaced by vertebral column in vertebrates) 2. Dorsal hollow nerve cord: A tubular nerve cord on the dorsal side 3. Pharyngeal gill slits: Openings in the pharynx (present in embryonic stage in many vertebrates) 4. Post-anal tail: An extension of the body beyond the anus
VI. Answer in Detail (5-mark questions)
Q1. Describe the salient features of phylum Porifera with examples.
Answer
Phylum Porifera (Sponges): Salient features: 1. Habitat: Mostly marine, some freshwater (e.g., Spongilla) 2. Symmetry: Mostly asymmetrical or irregular 3. Body organisation: Cellular level (no true tissues) 4. Body wall: Two layers — outer pinacoderm (with porocytes) and inner choanoderm (with collar cells/choanocytes) 5. Canal system: Water enters through ostia (pores), flows through the spongocoel (central cavity), and exits through the osculum. Types: Asconoid, Syconoid, Leuconoid 6. Skeleton: Made of spicules (calcium carbonate or silica) or spongin fibres 7. Nutrition: Holozoic — choanocytes create water current and trap food particles 8. Reproduction: Asexual (budding, gemmules) and sexual 9. Excretion: By diffusion through body wall Examples: Sycon, Spongilla (freshwater), Euspongia (bath sponge)
Q2. Compare the phyla Platyhelminthes and Aschelminthes (Nematoda).
Answer
| Feature | Platyhelminthes (Flatworms) | Aschelminthes (Roundworms) | |---|---|---| | Shape | Dorsoventrally flattened | Cylindrical, unsegmented | | Symmetry | Bilateral | Bilateral | | Germ layers | Triploblastic | Triploblastic | | Body cavity | Acoelomate | Pseudocoelomate | | Digestive system | Incomplete (no anus) | Complete (mouth and anus) | | Excretory organs | Flame cells | Rennet cells / canal system | | Circulatory system | Absent | Absent | | Sex | Mostly hermaphrodite | Dioecious (separate sexes) | | Segmentation | Absent | Absent | | Examples | Planaria, Liver fluke, Tapeworm | Ascaris, Wuchereria |
Q3. Describe the salient features of phylum Chordata and classify vertebrates.
Answer
Salient Features of Chordata: All chordates possess four key features at some stage of life: 1. Notochord: A dorsal, flexible rod supporting the body 2. Dorsal hollow nerve cord: A tubular nerve cord on the dorsal side 3. Pharyngeal gill slits: Openings in the pharynx (present in embryonic stage) 4. Post-anal tail: Extension of the body beyond the anus Classification of Vertebrata: 1. Class Pisces (Fishes): - Aquatic, streamlined body - 2-chambered heart, gills for respiration - Exoskeleton of scales - Oviparous (mostly) - Examples: Shark (cartilaginous), Rohu (bony) 2. Class Amphibia: - Dual life (aquatic larva, terrestrial adult) - 3-chambered heart, respiration by lungs and skin - Moist skin without scales - Oviparous, external fertilisation - Examples: Frog, Toad, Salamander 3. Class Reptilia: - Terrestrial, dry scaly skin - 3-chambered heart (partially 4 in crocodile) - Respiration by lungs - Oviparous, internal fertilisation, amniotic eggs - Examples: Snake, Lizard, Crocodile, Turtle 4. Class Aves (Birds): - Feathers, forelimbs modified as wings - 4-chambered heart, warm-blooded - Respiration by lungs with air sacs - Oviparous, beak, no teeth - Examples: Sparrow, Pigeon, Ostrich, Penguin 5. Class Mammalia: - Hair on skin, mammary glands (milk production) - 4-chambered heart, warm-blooded - Respiration by lungs - Most viviparous (except monotremes — egg-laying) - Examples: Human, Bat, Whale, Kangaroo
Common Mistakes to Avoid
- Calling sponges radially symmetrical: Sponges (Porifera) are mostly ASYMMETRICAL, not radially symmetrical. Cnidarians (jellyfish) are radially symmetrical.
- Confusing acoelomate and pseudocoelomate: Acoelomate = NO body cavity (Platyhelminthes). Pseudocoelomate = PARTIALLY lined cavity (Aschelminthes). Coelomate = FULLY lined cavity (Annelida, Chordata).
- Saying all chordates are vertebrates: Not all chordates are vertebrates. Protochordates (Hemichordata, Urochordata, Cephalochordata) are chordates without a vertebral column.
- Confusing Porifera canal system with circulatory system: Sponges have a water canal system for feeding, NOT a circulatory system. They don't have blood or blood vessels.
- Mixing up flame cells and nephridia: Flame cells are excretory organs of Platyhelminthes (flatworms). Nephridia are excretory organs of Annelida (earthworms).
- Forgetting that Arthropoda is the LARGEST phylum: About 80% of all animal species are arthropods (insects, spiders, crustaceans).
Exam Checklist
- [ ] Can you list the basis of animal classification (symmetry, germ layers, coelom, segmentation, notochord)?
- [ ] Can you distinguish between asymmetrical, radial, and bilateral symmetry?
- [ ] Can you explain diploblastic vs triploblastic animals with examples?
- [ ] Can you distinguish between acoelomate, pseudocoelomate, and coelomate?
- [ ] Can you describe the salient features of each phylum (Porifera to Chordata)?
- [ ] Can you distinguish between Platyhelminthes and Aschelminthes?
- [ ] Can you describe the four defining features of chordates?
- [ ] Can you classify vertebrates into 5 classes with distinguishing features?
- [ ] Can you give examples of each phylum?
- [ ] Can you identify which phylum has water vascular system, flame cells, and Malpighian tubules?
