How do you classify the "Perfect Organism"?

Hello there.

    Over the last few days, I have been enjoying a great deal of conversation with many of you concerning the Alien mythology and how it could possibly play into the upcoming Alien: Covenant. However, one question has worked its way to the fore of my thoughts: how does one classify the Alien? What type of animal is it - or to which animal group could it be most closely linked? It shares many aspects with both deep-water organisms, insects and reptiles, yet it can evidence a vast array traits that stem from its host. How would you classify it? As always, your thoughts and conjecture on this topic are most welcome, even if you choose to keep them to yourself. :)