Chapter 2 — Kingdom Animalia
Key Concepts — Major Phyla
| Phylum | Key feature | Example |
|---|
| Porifera | Pores (ostia), choanocytes, spicules | Sycon, Euspongia |
| Coelenterata (Cnidaria) | Nematocysts, radial symmetry, diploblastic | Hydra, Aurelia (jellyfish), Coral |
| Platyhelminthes | Flat body, acoelomate, hermaphrodite | Taenia (tapeworm), Fasciola (liver fluke), Planaria |
| Nematoda (Aschelminthes) | Round body, pseudocoelom | Ascaris, Wuchereria (filarial worm) |
| Annelida | Segmented body, true coelom (schizocoel) | Earthworm (Pheretima), Leech (Hirudo) |
| Arthropoda | Exoskeleton (chitin), jointed appendages | Cockroach, Butterfly, Crab, Scorpion |
| Mollusca | Soft body, mantle, shell, radula | Pila (apple snail), Octopus, Sepia |
| Echinodermata | Spiny skin, water vascular system, radial symmetry | Starfish (Asterias), Sea urchin |
| Chordata | Notochord, dorsal nerve cord, pharyngeal gill slits | Vertebrates (fish, frog, human) |
I. Choose the Best Answer (MCQs)
1. Choanocytes (collar cells) are characteristic of: (a) Coelenterata (b) Porifera (c) Platyhelminthes (d) Echinodermata
Answer(b) Porifera Choanocytes (collar cells) are flagellated cells lining the inner chambers of sponges. They create water currents for filter feeding — food particles are trapped by the collar and ingested. Unique to Porifera.
2. Nematocysts are found in: (a) Porifera (b) Platyhelminthes (c) Coelenterata (d) Annelida
Answer(c) Coelenterata (Cnidaria) Nematocysts are specialised stinging cells (cnidocytes) found only in Coelenterata. They are used for prey capture and defence. Each nematocyst contains a coiled thread that is discharged to sting and paralyse prey.
3. The water vascular system is a characteristic feature of: (a) Arthropoda (b) Mollusca (c) Annelida (d) Echinodermata
Answer(d) Echinodermata The water vascular system (ambulacral system) is unique to Echinodermata. It is a hydraulic system of water-filled canals connected to tube feet — used for locomotion, feeding, and respiration. Example: Starfish moves using sucker-tipped tube feet.
4. Which of the following is the largest phylum in the animal kingdom? (a) Chordata (b) Mollusca (c) Arthropoda (d) Annelida
Answer(c) Arthropoda Arthropoda is the largest phylum (~80% of all known animal species). Key features: exoskeleton (chitin), jointed appendages, segmented body, open circulatory system. Includes insects (most numerous class), arachnids, crustaceans, myriapods.
5. Which of the following shows true segmentation (metameric segmentation) and true coelom? (a) Platyhelminthes (b) Nematoda (c) Annelida (d) Echinodermata
Answer(c) Annelida Annelida has: true coelom (schizocoel — splits from mesoderm), true metameric segmentation (segments are similar; e.g. earthworm has ~100-120 segments), closed circulatory system, and setae for locomotion.
6. The distinguishing feature of Phylum Chordata is: (a) Exoskeleton (b) Notochord (c) Radula (d) Water vascular system
Answer(b) Notochord All chordates have (at some stage in life): notochord (flexible rod for support), dorsal hollow nerve cord, pharyngeal gill slits, post-anal tail. The notochord is replaced by the vertebral column in vertebrates.
7. Radula is the organ for feeding in: (a) Annelida (b) Echinodermata (c) Mollusca (d) Arthropoda
Answer(c) Mollusca Radula is a file-like feeding organ in most molluscs (except bivalves). It has rows of backward-curved teeth used to scrape food off surfaces. Example: Snails use radula to graze on algae.
II. Short Answer Questions
Q1. What are the distinguishing features of Phylum Arthropoda?
Answer
Arthropoda is the largest and most diverse phylum:
Key features: 1. Exoskeleton: Made of chitin; provides protection and support; must be shed during growth (moulting/ecdysis). 2. Jointed appendages: Paired, segmented limbs adapted for walking, swimming, flying, feeding. 3. Segmented body: Distinct head, thorax, and abdomen (insects); cephalothorax + abdomen (arachnids, crustaceans). 4. Open circulatory system: Blood (haemolymph) fills body cavity (haemocoel). 5. Compound eyes: Multiple lenses for wide field of vision. 6. Nervous system: Ventral nerve cord with ganglia.
Classes:
- Insecta: 3 pairs legs, 3 body segments, wings — Mosquito, Butterfly.
- Arachnida: 4 pairs legs, 2 body segments — Spider, Scorpion.
- Crustacea: 5+ pairs legs, hard exoskeleton — Crab, Prawn.
- Myriapoda: many legs — Centipede (Chilopoda), Millipede (Diplopoda).
Q2. List the differences between Coelenterata and Platyhelminthes.
Answer
| Feature | Coelenterata (Cnidaria) | Platyhelminthes |
|---|
| Body symmetry | Radial | Bilateral |
| Body layers | Diploblastic (ectoderm + endoderm; mesoglea in between) | Triploblastic (ecto + meso + endoderm) |
| Coelom | Absent | Absent (acoelomate) |
| Nematocysts | Present (unique) | Absent |
| Habitat | Mostly marine | Marine, freshwater, parasitic |
| Reproduction | Asexual + sexual; alternation of generations | Mostly hermaphrodite |
| Examples | Hydra, Aurelia, coral | Taenia, Fasciola, Planaria |
Q3. Describe the features of Phylum Echinodermata.
Answer
Echinodermata (Greek: echino = spiny; derm = skin) are exclusively marine animals.
Key features: 1. Spiny skin: Calcareous spines (CaCO₃) project through skin. 2. Water vascular system: Unique hydraulic system of canals → tube feet for locomotion, feeding, respiration. 3. Radial symmetry: Adult shows pentaradial (5-rayed) symmetry; larvae are bilaterally symmetrical. 4. No head: No cephalization; nervous system is a nerve ring. 5. Regeneration: Remarkable ability — a starfish arm can regenerate a new body. 6. Coelom: True coelom; no circulatory system (coelom fluid distributes materials). 7. Endoskeleton: Calcareous ossicles embedded in dermis.
Examples:
- Starfish (Asterias): 5 arms; predatory; water vascular system well developed.
- Sea urchin (Echinus): spherical; covered in spines; feeds on algae.
- Sea cucumber (Holothuria): elongated; used as food (Trepang).
- Brittle star (Ophiura), Feather star (Antedon).
Common Mistakes
- Saying Porifera are plants — they are multicellular animals (Metazoa).
- Confusing nematocysts (Coelenterata) and nematodes (Nematoda/Aschelminthes) — completely different things.
- Saying Echinodermata have bilateral symmetry — adults have pentaradial symmetry; larvae are bilateral.
- Forgetting that Arthropoda is the LARGEST phylum, not Chordata.
Exam Checklist
- Porifera: pores, choanocytes, spicules — Sycon, Euspongia.
- Coelenterata: nematocysts, radial, diploblastic — Hydra, Aurelia.
- Annelida: segmented, true coelom, setae — Pheretima (earthworm).
- Arthropoda: exoskeleton (chitin), jointed appendages — largest phylum.
- Echinodermata: water vascular system, spiny skin, pentaradial — Starfish.
- Chordata: notochord + dorsal nerve cord + pharyngeal slits + post-anal tail.
