Difference between Archaebacteria and Archaebacterium

What is the difference between Archaebacteria and Archaebacterium?

Archaebacteria as a noun is any primitive bacteria-like organism in the kingdom archaea. while Archaebacterium as a noun is any primitive bacteria-like organism in the kingdom archaea

We hope you now know whether to use Archaebacteria or Archaebacterium in your sentence.