Part 3 — Annelida, Arthropoda & Mollusca: Structure, Classification, Examples (Q.51–75)

Part 3 — Annelida, Arthropoda & Mollusca: Structure, Classification, Examples (Q.51–75)

Q51. Annelida (segmented worms) show:

A) Metamerism (true segmentation) with coelom divided by septa
B) No segmentation at all
C) Exoskeleton and jointed legs
D) Radial symmetry
Answer: A
Explanation:
A) Correct — earthworms show true metameric segmentation.
B–D) Incorrect.

Q52. In annelids, setae are used for:

A) Photosynthesis
B) Locomotion and anchorage in soil (bristles)
C) Feeding only
D) Gas exchange exclusively
Answer: B
Explanation:
A/C/D) Not primary functions.
B) Correct — setae help movement and grip.

Q53. The excretory organs of annelids are:

A) Flame cells
B) Protonephridia only
C) Metanephridia (paired nephridia in each segment)
D) Malpighian tubules
Answer: C
Explanation:
A/B) Flatworms.
C) Correct — metanephridia filter coelomic fluid and excrete waste.
D) In arthropods.

Q54. Which of the following is NOT a class of phylum Arthropoda?

A) Insecta
B) Crustacea
C) Cephalopoda
D) Arachnida
Answer: C
Explanation:
A/B/D) All arthropod classes.
C) Cephalopoda belongs to Mollusca.

Q55. Arthropods are successful because of:

A) Soft hydrostatic skeleton only
B) Chitinous exoskeleton, jointed appendages, segmentation, and tracheal/gill respiratory systems
C) Lack of segmentation
D) Radial symmetry
Answer: B
Explanation:
A/C/D) Incorrect.
B) Correct — these features enabled diversification and terrestrial adaptation.

Q56. In insects, gas exchange is primarily via:

A) Lungs
B) Gills
C) Tracheal system with spiracles and tracheae
D) Skin diffusion only
Answer: C
Explanation:
A/B) Not typical for insects.
C) Correct — network of tracheae delivers O₂ directly to tissues.
D) Some diffusion occurs but major system is tracheal.

Q57. Which structure is used by spiders for excretion?

A) Kidneys with nephrons
B) Malpighian tubules and coxal glands in some
C) Flame cells
D) Metanephridia
Answer: B
Explanation:
A) Vertebrate kidneys.
B) Correct — arthropods have Malpighian tubules; spiders also have coxal glands.
C/D) Other phyla.

Q58. Tagmatization (specialization of body regions) is well seen in:

A) Annelids only
B) Arthropods (head, thorax, abdomen)
C) Cnidarians
D) Poriferans
Answer: B
Explanation:
A) Annelids have segments but not strongly fused tagmata.
B) Correct — arthropods show distinct tagmata.
C/D) No tagmatization.

Q59. The radula is a characteristic organ of:

A) Arthropods
B) Molluscs, especially Gastropoda — a toothed organ for scraping food
C) Echinoderms
D) Annelids
Answer: B
Explanation:
A/C/D) Not correct.
B) Correct — radula used for feeding, absent in bivalves.

Q60. Which molluscan class includes squids and octopuses?

A) Gastropoda
B) Bivalvia
C) Cephalopoda (active predators with developed nervous system)
D) Polyplacophora
Answer: C
Explanation:
A) Snails/slugs.
B) Clams/oysters.
C) Correct — Cephalopoda (squid, octopus).
D) Chitons.

Q61. Bivalves (e.g., oysters) differ from gastropods (e.g., snails) by:

A) Presence of single shell vs two shells
B) Having two valves (bivalves), generally sedentary and filter-feeders vs gastropods with univalve shells and varied habitats
C) Having jointed legs
D) Possessing tracheal system
Answer: B
Explanation:
A) Reverse.
B) Correct — bivalves have two shells, are filter feeders; gastropods have one shell and diverse feeding.
C/D) Not molluscan.

Q62. Polychaetes (marine annelids) often have parapodia which serve as:

A) Respiratory and locomotive appendages
B) Reproductive organs only
C) Photosynthetic structures
D) Excretory organs
Answer: A
Explanation:
B–D) Incorrect.
A) Correct — parapodia bear setae and aid in locomotion and gas exchange.

Q63. Which arthropod group has book lungs?

A) Crustacea
B) Insecta
C) Arachnida (spiders) — book lungs for gas exchange
D) Myriapoda
Answer: C
Explanation:
A/B/D) Use gills/tracheae/other systems.
C) Correct — spiders have book lungs.

Q64. The arthropod exoskeleton is secreted by which tissue?

A) Intestine
B) Epidermis (hypodermis) secretes chitinous cuticle
C) Muscles
D) Nephridia
Answer: B
Explanation:
A/C/D) Not responsible.
B) Correct — epidermal cells secrete exoskeleton.

Q65. Circulatory system of most arthropods is:

A) Closed with arteries and veins like vertebrates
B) Open, with hemocoel and dorsal heart pumping hemolymph into sinuses
C) Absent
D) Based on tracheae only
Answer: B
Explanation:
A) Closed system is in annelids and vertebrates.
B) Correct — arthropods typically have open circulatory system.
C/D) Not correct.

Q66. Which mollusc secretes pearls?

A) Squid
B) Octopus
C) Oyster (bivalve) secretes nacre and may form pearls around irritants
D) Snail
Answer: C
Explanation:
A/B/D) Not pearl producers.
C) Correct — oysters and some bivalves can form pearls.

Q67. Arthropod growth involves moulting; the hormone responsible is:

A) Insulin
B) Ecdysone (molting hormone) produced by prothoracic glands in insects
C) Thyroxine
D) Adrenaline
Answer: B
Explanation:
A/C/D) Not involved.
B) Correct — ecdysone triggers ecdysis/ecdysis cycle.

Q68. Which annelid is earthworm, and what excretory organs does it have?

A) Earthworm (Lumbricus) — metanephridia in each segment
B) Earthworm — flame cells only
C) Earthworm — Malpighian tubules
D) Earthworm — nephridia absent
Answer: A
Explanation:
B) Flame cells are in flatworms.
C) Malpighian tubules in insects.
D) False — metanephridia present.
A) Correct.

Q69. Which arthropod class includes centipedes and millipedes?

A) Crustacea
B) Myriapoda (many legs, two main classes: Chilopoda – centipedes; Diplopoda – millipedes)
C) Hexapoda
D) Arachnida
Answer: B
Explanation:
A/C/D) Not centipedes/millipedes.
B) Correct — Myriapoda.

Q70. Gastropods undergo torsion during development, resulting in:

A) Loss of shell
B) Rotation of visceral mass causing mantle cavity to move near head — affects orientation of organs
C) Segmentation of body
D) Development of jointed appendages
Answer: B
Explanation:
A/C/D) Incorrect.
B) Correct — torsion is a 180° twist in gastropod larval development.

Q71. Which of the following is a terrestrial gastropod?

A) Octopus
B) Snail (e.g., Achatina)
C) Clam
D) Nautilus
Answer: B
Explanation:
A/C/D) Marine molluscs except some exceptions.
B) Correct — land snails are terrestrial gastropods.

Q72. Siphon in cephalopods is used for:

A) Feeding only
B) Jet propulsion and respiration (expels water for locomotion)
C) Photosynthesis
D) Excretion of solid waste
Answer: B
Explanation:
A/C/D) Incorrect.
B) Correct — siphon expels water enabling jet propulsion.

Q73. The major sensory organ in cephalopods (squid/octopus) resembling vertebrate eyes demonstrates:

A) Simple light sensitivity only
B) Image-forming, camera-type eye with complex retina — convergent evolution with vertebrates
C) Chemoreception only
D) No eyes present
Answer: B
Explanation:
A/C/D) Not fully correct.
B) Correct — cephalopod eyes are advanced, independent evolutionary development.

Q74. Which annelids have closed circulatory systems and well-developed hearts (aortic arches)?

A) Nematodes
B) Annelids like earthworms have closed system with dorsal/ventral vessels and aortic arches
C) Arthropods
D) Sponges
Answer: B
Explanation:
A/C/D) Not accurate.
B) Correct — annelids possess closed circulation with multiple aortic arches.

Q75. Which arthropod group primarily has two pairs of antennae?

A) Insects
B) Crustacea (e.g., prawns, crabs) — two pairs of antennae (antennules + antennae)
C) Arachnids
D) Myriapods
Answer: B
Explanation:
A) Insects have one pair.
B) Correct — crustaceans have two pairs.
C/D) No antennae as such. (more…)