This year Star Trek: Enterprise this year gave us an explanation of why Klingons look different in different series and thus cleared up a minor mystery.
It’s also cleared up something else: What a Tholian looks like.
In The Original Series, the Tholians appeared in just one episode ("The Tholian Web") and we never saw more than a weird-lookin’ face (?) on a viewscreen.
Folks naturally wonderd what the whole critter looked like, but until now we’ve never got to see.
Some even wondered whether the crystalline-lookin’ Tholian "face" we saw might be a helmet of some kind or if the critters were really crystalline.
The Tholians were almost totally ignored by later Star Trek series, though they were mentioned a number of times on Deep Space 9. A Tholian ambassador visited the station, though we never saw him. Capt. Sisko also had a conversation about (rare and much prized) Tholian "silk." And the Tholians signed a non-aggression pact with the Dominion before the war broke out. But for all the talk, we never got to see.
Now we have. In the two-part Mirror Universe episode "In A Mirror, Darkly," we finally get to see a Tholian.
Since both parts have now aired in all markets (and since this isn’t a matter of the plot and thus not a plot spoiler), I’ll go a head and show you a pic. Here ’tis:
As you can see, the ugly bugs are indeed crystalline. They also have six legs and two arms, which makes them arachnids.
There’s also a suggestion of motion under their crystalline carapace, which I s’ppose accounts for the weird color variations we saw on The Original Series’ viewscreen.
They live in a super-hot Venus-like environment.
So they’re blazingly hot crystal spiders.
Cool!
Only don’t say that to a Tholian. Probably won’t have the same resonance.
If you cool ’em off too much they start to crack. Need heat to live.
Tholian silk must be woven with asbestos or somethin.’
LEARN MORE ABOUT THOLIANS FROM MEMORY ALPHA (SPOILERS).