I once got irritated by a *stupid* mistake in "The Bestiary" (a section
of the *old* JTAS devoted to alien life forms). What set me off was a
reference to "copper-based hemoglobin".
I'm sure those of you with any acquaintance with biochemistry are
cringing now. :-) I did a bit of research and came up with a number of
possible "respiratory pigements" besides hemoglobin (and the
semi-well-known henocyanin).
I don't have the info anymore except what my trivia oriented mind
recalls. But I had *two* copper based. and a nickel based, and a
*different* iron-based one.
I liked the alternate iron-based pigment. I believe it was called
hemethryin (or something like that) it was pale pink when
non-oxygenated, and red when oxygenated. But what I liked best was the
minor little detail that could make a refs day.
It doesn't bind to the "respiratory poisons" that hemoglobin does.
Cyanide was *specificly* mentioned. I'm sure that the possibilities are
obvious to the devious refs out there... :-)
No doubt it is used by life forms on worlds with some sorts of "tainted"
atmosphere.