The correct answer is option 4, Mycoplasma.

Euglena, option 1, is a single-celled organism that belongs to the protist kingdom. It has a cell wall, which provides structural support and protection to the cell.

Paramecium, option 2, is also a single-celled organism belonging to the protist kingdom. It has a cell wall made up of tough, flexible microfibrils that help maintain the shape and protect the cell.

Gonyaulax, option 3, is a type of dinoflagellate, which are single-celled organisms with a cell wall made of cellulose. This cell wall is reinforced with plates that provide added protection.

Mycoplasma, option 4, is a unique bacterium that does not possess a cell wall. Instead, it has a flexible cell membrane that provides shape and protection to the cell. The absence of a cell wall makes Mycoplasma capable of changing its shape and allows it to easily pass through various environments. It is important to note that Mycoplasma is one of the few bacteria that lack a cell wall.

Therefore, among the given options, Mycoplasma is the organism that does not have a