Odd-one-out (life science) Which word does NOT belong with the others? Choose the single best answer.

Introduction / Context:
This classification question checks basic zoology. Four options are crustaceans (invertebrates with exoskeletons and jointed limbs), while one is a fish (a vertebrate). Recognizing taxonomic differences at a high level leads to the correct answer quickly.

Given Data / Assumptions:

• Options: eel, lobster, crab, shrimp, prawn
• Assume ordinary, non-technical common names.
• We need the single term that does not fit the crustacean group.

Concept / Approach:
Sort each animal by broad group. Crustaceans belong to subphylum Crustacea (arthropods). Fish are vertebrates; eels are elongated ray-finned fishes. Use this grouping to spot the outlier.

Step-by-Step Solution:

Verification / Alternative check:
Skeleton type and body covering: crustaceans have exoskeletons made of chitin and must molt; eels have internal skeletons and scales or smooth skin. Habitat overlap (marine or freshwater) does not change the taxonomic distinction, so the grouping remains valid.

Why Other Options Are Wrong:

• Lobster: classic crustacean; not a fish.
• Crab: crustacean; carapace and claws.
• Shrimp: crustacean; decapod.
• Prawn: crustacean; decapod, closely related to shrimp.

Common Pitfalls:
Confusing diet or habitat as the organizing principle. Many marine animals share habitats, but taxonomy by body plan and skeleton is the decisive criterion here.

Final Answer:
eel