Part 1 — Basics of Animal Classification, Levels of Organisation & Early Phyla (Q.1–25)

Part 1 — Basics of Animal Classification, Levels of Organisation & Early Phyla (Q.1–25)

Q1. The primary basis for dividing animals into different phyla is:

A) Habitat
B) Body plan and level of organization
C) Size
D) Food habit
Answer: B
Explanation:
A) Habitat — not primary (many phyla have species in multiple habitats).
B) Correct — body symmetry, germ layers, coelom, segmentation, organ systems are fundamental.
C) Size — irrelevant taxonomically.
D) Food habit — variable within phyla.

Q2. Animals showing bilateral symmetry are usually:

A) Diploblastic and sessile
B) Triploblastic and active
C) Asymmetrical and filter feeders
D) Radial and planktonic
Answer: B
Explanation:
A) Diploblastic & sessile — typical of some radially symmetrical animals (cnidarians).
B) Correct — bilateral symmetry correlates with cephalisation and active movement; triploblastic.
C) Asymmetrical — describes sponges.
D) Radial — describes cnidarians, echinoderms (adult).

Q3. Porifera differ from other animal phyla in that they:

A) Have true tissues
B) Lack true tissues and organs
C) Are triploblastic
D) Have a complete digestive tract
Answer: B
Explanation:
A) False — poriferans lack true tissues.
B) Correct — cellular level of organisation only.
C) False — not triploblastic.
D) False — no digestive tract; choanocytes filter feed.

Q4. The choanocytes (collar cells) of sponges function in:

A) Reproduction only
B) Locomotion of sponge
C) Creating water current and food capture
D) Excretion of wastes
Answer: C
Explanation:
A) Partial — contribute in sperm formation in some species but main role is feeding.
B) Sponges are sessile.
C) Correct — flagellum generates current; collar traps particles.
D) Excretion is diffusive.

Q5. Spicules in sponges are composed of:

A) Cellulose
B) Collagen only
C) Calcium carbonate or silica
D) Chitin only
Answer: C
Explanation:
A) Cellulose — not in sponges.
B) Collagen (spongin) occurs but spicules are mineral.
C) Correct — spicules are CaCO₃ or silica; spongin is organic matrix.
D) Chitin — found in arthropods.

Q6. Cnidarians (Coelenterata) are characterised by:

A) Complete digestive tract
B) Presence of cnidocytes and radial symmetry
C) Bilateral symmetry and segmentation
D) Cellular level organisation only
Answer: B
Explanation:
A) False — incomplete gut (gastrovascular cavity).
B) Correct — cnidocytes (nematocysts) and radial symmetry; diploblastic.
C) Bilateral & segmented — later animals.
D) They are tissue-level (diploblastic).

Q7. Which life forms exhibit alternation of polyp and medusa phases?

A) Most hydrozoans and scyphozoans
B) All poriferans
C) All flatworms
D) All echinoderms
Answer: A
Explanation:
A) Correct — e.g., Obelia, Aurelia show polyp/medusa alternation.
B–D) Incorrect — those phyla don’t have medusa forms.

Q8. Platyhelminthes (flatworms) show:

A) Coelom and segmentation
B) Acoelomate condition and bilateral symmetry
C) Radial symmetry and diploblastic organization
D) Notochord and dorsal nerve cord
Answer: B
Explanation:
A) False — lack coelom and segmentation mostly (except some annelid-like traits in tapeworm proglottids).
B) Correct — acoelomate, triploblastic, bilateral.
C) Radial/diploblastic — cnidarians.
D) Chordate features.

Q9. Which phylum contains organisms with a pseudocoelom?

A) Annelida
B) Platyhelminthes
C) Nematoda
D) Porifera
Answer: C
Explanation:
A) Annelids are coelomates.
B) Platyhelminthes are acoelomate.
C) Correct — nematodes have a pseudocoelom (body cavity not fully lined by mesoderm).
D) Porifera lack body cavity.

Q10. The distinguishing feature of rotifers is:

A) Presence of cnidocytes
B) Corona (ciliated wheel organ) for feeding
C) Segmentation into metameres
D) Jointed appendages
Answer: B
Explanation:
A) Cnidocytes — cnidarians.
B) Correct — rotifers have corona used for feeding and locomotion.
C) Segmentation — annelids.
D) Jointed appendages — arthropods.

Q11. Which germ layer gives rise to the nervous system in triploblastic animals?

A) Ectoderm
B) Mesoderm
C) Endoderm
D) Epidermis only
Answer: A
Explanation:
A) Correct — ectoderm forms nervous system and epidermis.
B) Mesoderm gives muscles, circulatory system, gonads.
C) Endoderm forms gut lining and associated organs.
D) Epidermis arises from ectoderm but answer too narrow.

Q12. Acoelomates are organisms that:

A) Have a true coelom
B) Have no body cavity between gut and body wall
C) Have a pseudocoelom lined with mesoderm
D) Have multiple coelomic compartments
Answer: B
Explanation:
A) Incorrect — that’s coelomate.
B) Correct — flatworms are acoelomate.
C) Pseudocoelomate — nematodes.
D) More complex coelomates like annelids may have compartments.

Q13. Which of the following is TRUE about protostomes?

A) Blastopore becomes anus
B) Spiral cleavage and determinate development often occur
C) Radial cleavage and indeterminate development
D) Notochord develops from ectoderm
Answer: B
Explanation:
A) Blastopore → mouth in protostomes (opposite in deuterostomes).
B) Correct — typical protostome pattern (e.g., molluscs, annelids, arthropods).
C) Radial/indeterminate — typical of deuterostomes.
D) Notochord — chordates (mesodermal).

Q14. Deuterostomes are characterised by:

A) Blastopore becoming mouth
B) Radial cleavage and blastopore becoming anus
C) Lack of coelom
D) Always having segmentation
Answer: B
Explanation:
A) Protostome trait.
B) Correct — deuterostomes (echinoderms, chordates) show radial cleavage and blastopore → anus.
C) Many deuterostomes are coelomate.
D) Segmentation occurs in annelids, arthropods, chordates (not universal).

Q15. Which phylum includes species that have a single opening serving as mouth and anus?

A) Annelida
B) Cnidaria
C) Arthropoda
D) Echinodermata
Answer: B
Explanation:
A) Annelids have complete digestive tract.
B) Correct — cnidarians have gastrovascular cavity with single opening.
C, D) Both have complete alimentary canals.

Q16. Pseudocoelomic fluid in nematodes primarily serves as:

A) A hydrostatic skeleton and medium for transport
B) Reproductive organ
C) Photosynthetic organ
D) Sensory organ
Answer: A
Explanation:
A) Correct — hydrostatic skeleton and distribution of nutrients/wastes.
B–D) Incorrect.

Q17. Which of the following non-chordate phyla shows segmentation?

A) Platyhelminthes
B) Annelida
C) Porifera
D) Cnidaria
Answer: B
Explanation:
A) Mostly unsegmented (except pseudosegmentation in tapeworm proglottids).
B) Correct — annelids are segmented (metameric).
C) Sponges not segmented.
D) Cnidarians show radial symmetry, not segmentation.

Q18. Flame cells (protonephridia) are excretory structures of:

A) Annelids
B) Platyhelminthes
C) Arthropods
D) Molluscs
Answer: B
Explanation:
A) Annelids have metanephridia.
B) Correct — flame cells function in flatworms (planaria).
C, D) Different excretory systems.

Q19. Which feature is diagnostic for Phylum Porifera?

A) Cnidocytes
B) Choanocytes and canal system
C) Radula
D) Mantle
Answer: B
Explanation:
A) Cnidocytes — cnidarians.
B) Correct — choanocytes and aquiferous system are sponge features.
C) Radula — molluscs (gastropods).
D) Mantle — molluscs.

Q20. In simple animals, gas exchange mainly occurs by:

A) Lungs
B) Gills only
C) Diffusion across body surface
D) Tracheal system
Answer: C
Explanation:
A/B/D) Specialized respiratory organs in higher animals.
C) Correct — small/simple animals rely on diffusion across moist surfaces.

Q21. Which is an example of acoelomate animal?

A) Earthworm (Annelida)
B) Tapeworm (Platyhelminthes)
C) Roundworm (Nematoda)
D) Squid (Mollusca)
Answer: B
Explanation:
A) Earthworm is coelomate.
B) Correct — tapeworms are acoelomate.
C) Nematodes are pseudocoelomate.
D) Molluscs are coelomate.

Q22. The developmental fate “determinate cleavage” is associated with:

A) Deuterostomes
B) Protostomes
C) Radial cleavage organisms
D) All animals
Answer: B
Explanation:
A) Deuterostomes show indeterminate cleavage.
B) Correct — protostomes often have determinate (mosaic) cleavage.
C) Radial cleavage is deuterostome trait.
D) Not universal.

Q23. Which of the following phyla shows a water vascular system?

A) Annelida
B) Echinodermata
C) Arthropoda
D) Mollusca
Answer: B
Explanation:
A) Annelids have coelomic fluid-driven locomotion.
B) Correct — echinoderms have water vascular system with tube feet.
C, D) No water vascular system.

Q24. Which animals are primarily filter feeders among the given?

A) Many Poriferans and some Molluscs (bivalves)
B) All Arthropods
C) All Annelids
D) All Platyhelminthes
Answer: A
Explanation:
A) Correct — sponges and bivalves filter particles from water.
B–D) Not generally filter feeders.

Q25. Which of the following is TRUE about coelom?

A) It always indicates primitive organization
B) It is a body cavity lined by mesoderm in true coelomates
C) It is absent in annelids
D) It is the same as pseudocoelom
Answer: B
Explanation:
A) False — coelom indicates more advanced body plan.
B) Correct — true coelom is mesoderm-lined cavity.
C) False — annelids have coelom.
D) False — pseudocoelom is not fully mesoderm-lined. (more…)