Identify the correct order of known species of organisms by their...

The approximate number of known and described species for different groups of organisms is as follows:

Eubacteria: $\sim 10,000$
Protists: $\sim 60,000$
Fungi: $\sim 100,000$
Plants: $\sim 300,000$
Animals: $> 1,200,000$

Arranging them in increasing order of their known species numbers, we get:
Eubacteria \rightarrow Protists \rightarrow Fungi \rightarrow Plants \rightarrow Animals.

Answer: Eubacteria - Protists - Fungi - Plants - Animals