Question

which organisms are called primitive and how are they different from the so-called advanced organisms

Answer 1

an organism which is went back to its primary form is called primitive organism.
an organism which evolves into better form are called advanced organism

Answer 2

The organisms present on Earth on starting age of life (in sea or in ocean or in any water bodies) is called as Primitive. This is a lot of diffrrence between primitive and modern organism by avability of
1.food
2.cloth
3.shelter
4.technology