**Introduction:**
Prokaryotes are a group of organisms that lack a membrane-bound nucleus and other membrane-bound organelles. They are unicellular organisms that include bacteria and archaea. Prokaryotes have a cell wall that provides structural support and protection. However, there is one group of prokaryotes that is wall-less, known as Mycoplasma.

**Mycoplasma:**
Mycoplasma is a genus of bacteria that belong to the class Mollicutes. They are unique among prokaryotes because they lack a cell wall. Instead, they have a flexible cell membrane that gives them a pleomorphic (varying in shape) appearance. This absence of a cell wall makes Mycoplasma highly adaptable, allowing them to colonize a wide range of environments, including the human body.

**Bacteria:**
Bacteria are prokaryotic microorganisms that have a cell wall made up of peptidoglycan. The cell wall provides shape, protection, and structural support to the bacteria. It helps them withstand changes in osmotic pressure and prevents them from bursting. The cell wall also plays a role in bacterial pathogenesis, as it can interact with the host immune system.

**Cyanobacteria:**
Cyanobacteria, also known as blue-green algae, are a group of photosynthetic prokaryotes. They have a cell wall that contains peptidoglycan and other complex polysaccharides. The cell wall provides them with structural support and protection. Cyanobacteria are capable of oxygenic photosynthesis and are responsible for the production of a significant amount of the Earth's oxygen.

**Slime molds:**
Slime molds are not prokaryotes but rather a type of eukaryotic organism. They belong to the kingdom Protista and are known for their unique life cycle. Slime molds can exist as free-living single-celled amoeboid organisms or as a multicellular mass called a plasmodium. They do not possess a cell wall like prokaryotes or most other eukaryotes.

**Conclusion:**
Among the options given, Mycoplasma is the only wall-less prokaryote. Bacteria and cyanobacteria have cell walls, while slime molds are not prokaryotes. Mycoplasma's lack of a cell wall gives it unique characteristics and allows it to thrive in various environments.