Q.139 Zoology ⭐ 360° Option Elimination Active
NEET 2025 Zoology Question 139 Solution
Topic: Animal Kingdom · Official NTA Booklet Code 45
Question
All living members of the class Cyclostomata are:
✓
Verified Against NTA Final Answer Key
Option (4) : Ectoparasite
📚 Animal Kingdom Easy
📋 Given Parameters & Problem Setup
Class Cyclostomata (jawless vertebrates, e.g. Petromyzon, Myxine)
Target Feature Mode of living / nutrition of all living members
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⏱️ Save ~15 seconds The 30-Second Exam Hall Shortcut: ⚡ Cyclostome Lifestyle Fingerprint
Class Cyclostomata: "All living members of the class Cyclostomata are ECTOPARASITES on some fishes!" Suctorial circular jawless mouth attaches to fish hosts!
1 Recall the opening sentence of NCERT Section 4.2.11.1 (Class - Cyclostomata):
2 - "All living members of the class Cyclostomata are ectoparasites on some fishes."
3 - They have an elongated body bearing 6-15 pairs of gill slits for respiration.
4 - They have a sucking and circular mouth without jaws.
5 - Examples: Petromyzon (Lamprey) and Myxine (Hagfish).
6 Direct answer: Ectoparasite!
7 Select Option (4)!
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Why You Can 100% Trust This Shortcut: Aves Characteristic Skeletal & Respiratory Adaptations (NCERT Biology · Animal Kingdom: Pneumatic bones and air sacs).
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Step-by-Step Rigorous Workflow & Mathematical Proof
Step 1
Taxonomic Position of Cyclostomata
Cyclostomes belong to Subphylum Vertebrata, Division Agnatha (animals lacking jaws):
- • They represent the only surviving jawless vertebrates.
- • Living representatives include lampreys (*Petromyzon*) and hagfishes (*Myxine*).
Step 2
Nutritional Adaptation and Parasitic Habit
Morphological specializations for their lifestyle:
- • NCERT states unequivocally: "All living members of the class Cyclostomata are ectoparasites on some fishes."
- • They possess a ventral, circular, jawless mouth modified into a powerful suctorial disc equipped with horny epidermal teeth.
- • They attach to the lateral body surfaces of larger teleost fishes, rasps their flesh, and suck their blood and body fluids as obligate ectoparasites.
Step 3
Conclusion
All living cyclostomes are categorized ecologically and physiologically as Ectoparasites.
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4-Option Deep Scan
360° Option Elimination Engine Key Feature
Diagnose every choice: Know exactly why the right option works and why distractors fail.
1 A
✗ Incorrect Verdict & Scientific Reason:
Incorrect. Adult cyclostomes are not free-living predators; they are specialized ectoparasites attached to fishes.
⚠️
Student Fallacy (Why candidates pick this trap): Confusing free-swimming larval stage (ammocoetes) with adult lifestyle.
2 B
✗ Incorrect Verdict & Scientific Reason:
Incorrect. They live on the outer surface of fish hosts, not inside internal tissues or gut.
⚠️
Student Fallacy (Why candidates pick this trap): Confusing external feeding with internal parasitism.
3 C
✗ Incorrect Verdict & Scientific Reason:
Incorrect. The relationship is strictly parasitic (+, -), causing harm and death to the fish host.
⚠️
Student Fallacy (Why candidates pick this trap): Misinterpreting host attachment as mutualism/commensalism.
4 D
✓ 100% Correct Verdict & Scientific Reason:
100% correct. Direct verbatim NCERT fact: "All living members of the class Cyclostomata are ectoparasites on some fishes."
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Why this is airtight: None; textbook recall.
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NTA Trap Alert: Universal Qualifier "All living members"
Questions beginning with "All..." often trigger caution in students, but here NCERT explicitly uses the absolute phrasing: "All living members of the class Cyclostomata are ectoparasites on some fishes." Do not doubt this absolute statement!
🛡️ How to avoid the -1 mark: Remember NCERT verbatim: ALL living cyclostomes are ECTOPARASITES.
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Core NEET Syllabus Standard
NEET Biology Core Syllabus · Animal Kingdom Standard Benchmark
Core Scientific Principle Tested:
"All living cyclostomes are ectoparasites on fishes with a circular, jawless, sucking mouth."
Syllabus Focus: Class Cyclostomata
✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗
CYCLO-STOMA = Sucks onto fish skin from the outside (ECTO-parasite)!
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