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Q74 (IAS/2014) Science & Technology › Basic Science (Physics, Chemistry, Biology) › Animal diversity behaviour Official Key

Among the following organisms, which one does not belong to the class of other three?

Result
Your answer: —  ·  Correct: A
Explanation

Crabs are crustaceans[1], while mites, scorpions, and spiders are all arachnids[4]. These are different classes within the phylum Arthropoda. Arthropods include crustaceans, insects, and arachnids[6], making them distinct taxonomic groups.

Arachnids do not have antennae and have 2 body parts and 4 pairs of legs[3], whereas crustaceans have a hard, external shell which protects their body[1] and possess different anatomical features. The key distinction is that crab belongs to class Crustacea while mite, scorpion, and spider all belong to class Arachnida. Therefore, the crab is the organism that does not belong to the class of the other three.

Sources
  1. [1] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 9: Indian Biodiversity Diverse Landscape > Crustaceans > p. 155
  2. [2] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 9: Indian Biodiversity Diverse Landscape > Arachnids > p. 156
  3. [3] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 9: Indian Biodiversity Diverse Landscape > Arachnids > p. 156
  4. [4] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 9: Indian Biodiversity Diverse Landscape > Arachnids > p. 156
  5. [5] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 9: Indian Biodiversity Diverse Landscape > Arthropods > p. 155
  6. [6] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 9: Indian Biodiversity Diverse Landscape > Arthropods > p. 155
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Q. Among the following organisms, which one does not belong to the class of other three? [A] Crab [B] Mite [C] Scorpion [D] Spider
At a glance
Origin: From standard books Fairness: High fairness Books / CA: 10/10 · 0/10
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This is a classic 'General Science meets Environment' question. It rewards basic observation over rote memorization. If you read the introductory pages of the Biodiversity chapter in standard texts (like Shankar IAS), the distinction between Arachnids and Crustaceans is explicitly listed. Do not skip the 'Basics of Life' section thinking it is too elementary.

How this question is built

This question can be broken into the following sub-statements. Tap a statement sentence to jump into its detailed analysis.

Statement 1
What is the biological taxonomic class of crabs?
Origin: Direct from books Fairness: Straightforward Book-answerable
From standard books
Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 9: Indian Biodiversity Diverse Landscape > Crustaceans > p. 155
Presence: 5/5
“• Most live most ly in the ocean or other waters.• Have a hard, external shell which protects their body• Most commonly known crustaceans are the crab, lobster and barnacle.”
Why this source?
  • Explicitly lists crab alongside lobster and barnacle as the most commonly known 'crustaceans'.
  • Directly links the common name 'crab' to the group label 'crustaceans', supporting identification of crabs as crustaceans.
Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 3: MAJOR BIOMES > Classifcation of marine ecosystems > p. 31
Presence: 4/5
“Tese are found in all oceanic depths. At diferent landforms of the seashore, there develop numerous types of fauna and fora. Crabs, crustaceans are important in the seashore, who make holes in the sea-sand. A large number of birds feed on their prey by probing into the sand or mud on the seashore. Several species of fsh and grasses are also found in the coastal ecosystems. Te numerous fauna and fora species are confned and concentrated along the photic zone. Te communities include planktons, phytoplanktons and diatoms. Algae and diatoms are the most important species of phytoplankton communities. Numerous types of bacteria are also found in the pelagic biome. (ii) Benthic Biome: It is the zone of the ocean bottom.”
Why this source?
  • Pairs the words 'Crabs, crustaceans' in describing seashore fauna, reinforcing that crabs are members of the crustacean group.
  • Describes ecological role of crabs as 'crustaceans', providing contextual support for their taxonomic grouping.
Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 9: Indian Biodiversity Diverse Landscape > 9.2.2. Invertebrates > p. 154
Presence: 3/5
“Invertebrates do not have backbones. More than 98% of animal species in the world are invertebrates. Invertebrates don't have an internal skeleton made of 154 All Rights Reserved. No part of this material may be reproduced in any form or by any means, without permission in writing.”
Why this source?
  • Explains the broader category 'invertebrates' (animals without backbones), into which crustaceans — and thus crabs — fall.
  • Places crabs within larger taxonomic/functional groupings used in the snippets, supporting classification context.
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Statement analysis

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