|image=FileOf protozoa close.jpg|250px
The '''protozoan''' is an inoffensive entity seen on Xen.
*The Protozoan appears as a bluish, transparent rock-like entity orbiting above the ground, with a smaller reddish rock-like shape inside, also transparent and turning on itself. It has no AI, cannot be destroyed and does not react to the player's or any NPC's presence.
*It is first seen in ''Half-Life'' for a few seconds during the Resonance Cascade, orbiting behind two Bullsquids drinking from a Healing Pool. It is also seen in the same map in ''Half-Life Opposing Force|Opposing Force'' (reached several times with the Displacer Cannon) as well as ''Half-Life Decay|Decay'', at the very start of the bonus chapter, ''Xen Attacks''.
==Behind the scenes==
The "protozoan" (Gr. "prôtos", "first" + "zôon", "animal"), also named "protozoon", actually exists. It covers any of a large group of single-celled, usually microscopic, WikipediaEukaryote|eukaryotic WikipediaProtist|protist organisms commonly living in water, such as WikipediaAmoeba (genus)|amoebas, WikipediaCiliate|ciliates, WikipediaFlagellate|flagellates, and WikipediaApicomplexa|sporozoans.
[http//www.thefreedictionary.com/protozoan Protozoan on The Free Dictionary] Protozoa can be plants, fungi or animals. Thus the Protozoan can be considered as an extremely enlarged protozoan that does not live underwater.
*"Protozoa", the model name, is actually the plural form.
*When viewing its model in a model viewer, it is completely opaque. Its transparency is achieved in-game.
FileProtozoa model inside.jpg|Inside the Protozoan model.
FileC1a0e pool.jpg|In ''Half-Life''.
FileBullsquid Xen Op4.jpg|Same area in ''Opposing Force''.
==List of appearances==
*''Half-Life Opposing Force''
CategoryHalf-Life Opposing Force