Which one of the following living organisms completely lacks a cell wall?

Gorgonia belongs to cnidaria class- Anthozoa (animal). Gorgonians are also known as sea whips or sea fans and are similar to the sea pen, a soft coral. These marine invertebrates are multi-cellular, have no cell walls (a characteristic of plants), most have tissues (organized groups of cells), and all are heterotrophic, i.e., they cannot manufacture their own food and depend on other organisms for nutrition. So, the correct answer is 'Sea-fan (Gorgonia)'