Background information Edit
The Zaranites were designed by Fred Phillips and Robert Fletcher for The Motion Picture. In addition to creating numerous new species for the film, Fletcher took his design talents a step further and "not only named these creatures but, with the approval and guidance of Gene Roddenberry, providing complete backgrounds for each." The following is a brief description, in Fletcher's own words:
"ZARANITES – Can't breath oxygen, so must wear breathing mask on Earth; pack on back generates fluorine gas which they breathe. Costume: old suedes found in Paramount storage, left over from DeMille's The Ten Commandments. Jewelry: hornlike in appearance, supposedly made of horns of one of the most widely cultivated Zaranite animals, the Berbbotjahaa. Actually made from fabric and liquid plastic. Represents family totem. Top part (necklace) designates family, lower is personal designation." (The Making of Star Trek: The Motion Picture, p. 130)
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." 
Word-for-word portions presented in Fletcher's initial description above would later be excised in an article appearing in the January 2002 edition of Star Trek: The Magazine Volume 2, Issue 9, entitled "Who is that Alien?", which in addition, likens the Zaranites to the Benzites.
The Zaranite breathing apparatus from The Motion Picture was reused for a pair of Aammazaran Federation Councilors at James T. Kirk's trial in Star Trek IV: The Voyage Home (though they themselves were actually referred to in Star Trek IV Sourcebook Update as Zaranites) and as Camp Khitomer attendees in Star Trek VI: The Undiscovered Country. Neither variations were described as specifically being Zaranites (except for the pair of Federation councilors, in the Star Trek IV Sourcebook Update).
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.