Background information Edit
In an interview with Robert Fletcher – published in the February 1980 edition of Fantastic Films, as part one of a two-part interview with him, called "The Star Trek Costumes" – the Zaranites were described thus;
"Unable to breathe oxygen, they are forced to wear breather masks on any planet which does not have a fluorine gas atmopshere [sic]. They have packs on their backs which carry a mechanism capable of generating this gas. To know any Zaranite's history one has only to translate the jewelry which he or she wears around the top half of the body while the lower part signifies their personal designation. Because their home world is poor in precious metals, all adornment is produced from the horns of their most widely cultivated animal – the Berbbotjahaa." 
In an article appearing in the January 2002 edition of Star Trek: The Magazine Volume 2, Issue 9, entitled "Who is that Alien?", the following information about the Zaranites, based on Robert Fletcher's original background notes, added:
Like the Benzites, the Zaranites could not breath oxygen. In order to survive on Class-M worlds, they used breathing masks and backpacks that supplied them with fluorine gas. The jewelry they wore was made from horns of the Berbbotjahaa; the top part of the necklace indicated their family, while the bottom identified each individual.
The Zaranite breathing apparatus from The Motion Picture was reused for a pair of Federation councilors at Kirk's trial in Star Trek IV: The Voyage Home and as Camp Khitomer attendants in Star Trek VI: The Undiscovered Country, whereas the aforementioned missing headpiece reappeared for an alien design only known as "Dark Eyes" in Star Trek V: The Final Frontier. In both cases, it is unclear if these individuals were intended to represent Zaranites or other unknown species.
According to Star Trek: Star Charts (United Federation of Planets I), Zaran (Mu Capricorni) was the name of a star in the Alpha Quadrant. The primary was a Class F star. The magnitude of this star was +5, which was the same brightness as Sol. This was a Federation system, with at least one planet being an affiliate.
Zaranites were featured in the novel Triangle from Pocket Books, although no mention was made of the background information from the films. The novel names their homeworld Zaran II, a name later supported by Star Trek: Star Charts.
Zaranites also occasionally appeared in the Star Trek newspaper comic strip.