Correct Answer: Plasmodium

Solution : The correct answer is Plasmodium .

Plasmodium belongs to the phylum Apicomplexa. This parasitic protozoan is responsible for causing malaria in humans. The characteristic feature of organisms in the phylum Apicomplexa is the presence of an apical complex, a specialised structure involved in host cell invasion. Unlike sponges, Physalia (Portuguese Man-of-War), and Hydra, which belong to other phyla, Plasmodium is specifically classified within Apicomplexa due to its unique biological and morphological characteristics.