Protoplasmic - Level of body organization
Organisms which are made of just one cell are the simplest and the most primitive creatures called unicellular organisms. Their level of body organization is at the lowest and is called protoplasmic level of body organization. If we try and fit the metazoan body organization into a pyramid mode, the protoplasmic level will be at the bottom. As the organisms evolved from unicellular to multicellular grade their level of body organization also changed from simple to complex.
Figure: Level of Body Organization