I. They mean "first animals".

Here are ten salient characteristics of Protozoa:

i. They mean "first animals".
ii. They are unicellular.
iii. They are microscopic (except for shelled Foraminiferans).
iv. They are the simplest and most primitive.
v. They are the first of the lower invertebrates.
vi. They have no backbones.
vii. They have no coelomic cavities.
viii. They have no germ layers, tissues, or organs.
ix. They are at the protoplasmic level of organization (sometimes called non-cellular).
x. They possess functional intricate organelles that carry out division of labor.