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

The organism that is not classified as an animal is "Euglena." Animals are a diverse group of multicellular organisms that belong to the kingdom Animalia. They are characterized by their ability to move, consume organic matter as a source of nutrition, and lack of cell walls. Amoeba, Paramecium, and Obelia are all classified as animals. Amoebas and Parameciums are single-celled organisms that are classified as protozoans, which are a type of animal-like protist. Obelia is a colonial animal that belongs to the phylum Cnidaria, which also includes jellyfish and coral. Euglena, on the other hand, is a unicellular organism that is classified as a protist. Although it possesses some animal-like characteristics, such as the ability to move and consume organic matter, it also possesses features that are more typical of plant-like organisms, such as the presence of chloroplasts for photosynthesis. Therefore, the correct answer is "Euglena" because it is not classified as an animal, but rather as a protist.