Well damn, that is pretty oblique. I didn't realize that was a reference. Hm. Was "Tuvix" ever referenced afterwards?
The word is poikilothermic, and it refers to an organism whose body temperature is variable (i.e. what's inaccurately called a "cold-blooded" creature in vernacular). Amphibians are poikilotherms, but so are fish, reptiles, many invertebrates, and even naked mole rats (the only known mammalian ones).
Well, at least in this instance my science officer told me the D'Arsay where both amphibian and poikliothermic. Where the Hranrarii poikliotherms as well, I wonder?
Probably some of those mediocre episodes buried in the middle of seasons of TNG, DS9, VOY, and ENT. I was going to say Code of Honor, then I realized that Dark Mirror had the Mirror Ent-D sterilize one of their continents.
I think at least one of the numbered DS9 novels referenced it. I know a lot of S1 episodes were referenced, but I can't be sure if Move Along Home was an exception.
Referenced in Rising Son, when Jake remembers his father being a bit iffy on the subject of the Wadi, which he didn't understand given that the Wadi weren't Dominion members. PS: Here's hoping the political cold war between the Typhon Pact and the Khitomer Accords will be resolved with an epic Chula game played by each nation's representatives or leaders.
Nobody's mentioned whether "Tuvix" is later referenced. I wouldn't be surprised if it was, but I'm not aware of it happening.
Was TNG's "Transfigurations" (Season 3) ever referenced? I always thought the Zalkonians were somewhat interesting, but to my knowledge, they have never appeared in TrekLit.
How about "The Man Trap"? With the possible exception of Trelane's stuffed-and-mounted salt vampire (that was probably just a budgetary thing), the only thing I can think of that references it, whether on screen or in print, is my own student short story, Inteview with Dr. Ambrose Crater, or "The Salt Vampire Ate My Parents."
Nancy Crater nee Bierce appears in flashbacks in A Choice of Catastrophes. I'd be really surprised if there's a single unreferenced TOS episode. It's got to be a late-series VOY episode, if anything. "Live Fast and Prosper"?
I've referenced the Acamarians and/or the Gatherers in The Buried Age and Forgotten History. And Acamar III was mentioned in both Greater Than the Sum and Destiny as one of the first planets wiped out in the Borg invasion (though that reference originated with Dave, not me).