Which if the following organisms is not classified as an animal?

Step 1: Analyze the question We are asked to pick the organism that is not classified as an animal. Think about which one has plant-like features.

Step 2: Explain the concept Classification often depends on how an organism feeds and what structures it has:

• Animals feed heterotrophically (they take in ready-made food) and have no chloroplasts.
• Plant-like organisms contain chloroplasts with chlorophyll and make food by photosynthesis (autotrophic).

In traditional Nigerian secondary school biology, unicellular organisms such as Amoeba and Paramecium are treated as protozoans (animal-like protists). Obelia is a true multicellular animal, a coelenterate (cnidarian).

Step 3: Go through the options

• A. Amoeba: a protozoan that feeds by engulfing food (phagocytosis). It is animal-like.
• B. Paramecium: a ciliated protozoan that feeds heterotrophically. It is animal-like.
• C. Euglena: a unicellular organism with chloroplasts. It photosynthesizes in light, like a plant, but can also feed on organic matter in the dark. It also has a flagellum and an eyespot. Because of this mixed nature, it is classified as a protist, often grouped with algae (plant-like), and not as a true animal.
• D. Obelia: a colonial marine coelenterate. It is a true animal.

Step 4: Answer The organism not classified as an animal is Euglena, which is option C.

Tip: Remember "Euglena = Green". If an organism in the list has chloroplasts, it is the odd one out among animal-like organisms. Euglena is the classic WASSCE and JAMB example of an organism that shows both plant and animal features.