Which one of the following pairs, describing an organism and the organ or part that helps in its locomotion, is NOT correctly matched?

Introduction / Context:
Different organisms use different structures for locomotion depending on their body plan and environment. Many exam questions ask you to match organisms with the correct locomotory organ. This question gives four pairs and asks you to identify the pair that is not correctly matched, that is, where the stated locomotory organ is wrong for that organism.

Given Data / Assumptions:

• The organisms mentioned are Euglena, Paramecium, Nereis, and starfish.
• The locomotory structures listed are flagellum, cilia, pseudopodia, and tube feet.
• We assume standard zoology classifications for these organisms.

Concept / Approach:
Euglena is a unicellular, flagellated protist that moves primarily with a whip like flagellum. Paramecium is a ciliated protozoan that uses many tiny cilia for locomotion. Starfish (sea stars) are echinoderms that move using tube feet operated by a water vascular system. Nereis, however, is a segmented marine worm (polychaete) that moves using parapodia, which are paired, fleshy, paddle like appendages, not pseudopodia. Pseudopodia are temporary cytoplasmic projections used for movement by amoeboid organisms such as Amoeba, not by Nereis. Therefore, the pair “Nereis : Pseudopodia” is the mismatched one.

Step-by-Step Solution:
Step 1: Evaluate option A, Euglena : Flagellum. This is correct as Euglena moves mainly using a whip like flagellum.Step 2: Evaluate option B, Paramecium : Cilia. This is correct because Paramecium swims using coordinated beating of cilia covering its surface.Step 3: Evaluate option C, Nereis : Pseudopodia. Nereis is an annelid worm with parapodia, not pseudopodia. Pseudopodia are characteristic of amoeboid cells.Step 4: Evaluate option D, Starfish : Tube feet. This is correct as starfish locomotion relies on tube feet powered by the water vascular system.Step 5: Identify option C as the only incorrect pairing.

Verification / Alternative check:
A quick way to verify is to recall textbook images: Euglena with a long flagellum at one end, Paramecium covered in cilia, Amoeba with changing pseudopodia, and starfish with rows of tube feet on the underside of arms. Nereis, drawn as a segmented worm with fleshy lateral extensions (parapodia), clearly does not use pseudopodia. This confirms that the Nereis pair is wrong.

Why Other Options Are Wrong as Answers:
Option A is a correct pair, so it cannot be the answer to “not correctly matched.” Option B is also a correct pair and must be rejected as a wrong match. Option D is correct because tube feet are the proper locomotory structures of a starfish. Only option C mislabels the locomotory structure for Nereis.

Common Pitfalls:
Students sometimes focus on the similarity of terms like “pseudopodia” and “parapodia” and assume they refer to the same structure. In reality, pseudopodia are temporary cell extensions used by unicellular organisms, while parapodia are permanent paired outgrowths of some worms. To avoid confusion, remember that “pseudo-” means false and is linked with Amoeba, while “para-” in parapodia suggests structures alongside the body segments of a worm like Nereis.

Final Answer:
Nereis : Pseudopodia.