Chilomonas are small, from 20-40µm long.

The mastigophora all have one thing in common. They have flagella or flagellum (hence, they as a group are sometimes called "flagellates"). These whip like extensions are composed of a complex arrangement of protein microtubules. Some sources use the word "undulipodium" to identify the flagellum and differentiate it from that of bacteria.

Chilomonas are very common and are one of the chief food sources for larger protozoans, especially Amoeba proteus.