Each of the three species native to the Beta Rigel (Tau-3 Eridani) star system possessed a different reproductive system. That led to confusion among outsiders about the number and nature of Rigelian sexes. The Chelons of Beta Rigel III were hermaphrodites, the Jelna of Beta Rigel V included two varieties for male and female each, and the Zami and Kalar of Beta Rigel IV and Beta Rigel VII, respectively, were typical binary-gendered. Combining all three species, there were a total of five different sexes among the Rigelians. (ENT episode: "Cogenitor"; ENT - Rise of the Federation novel: Tower of Babel)
Chelons
Chelons were a hermaphroditic species, like the Hermats, i.e possessing a single sex. Unlike them, most of them assumed a binary gendered identity, choosing to present themselves as either male or female. The more traditional inhabitants of the Hainali Basin on Beta Rigel III rejected that notion and were proud of their hermaphroditic nature. An openly hermaphroditic Chelon was addressed as Velom. (ENT - Rise of the Federation novel: Tower of Babel) Examples for differently gendered Chelons include Velom Ganaiar, the female Federation Councilor Kishkik Sajithen and the male Federation Ambassador Jetanien. (ENT - Rise of the Federation novel: Tower of Babel; VAN novel: Harbinger)
Jelna
The Jelna had four visually distinguishable sexes. The exosexes possessed an extra Z chromosome and outnumbered the endosexes by 2 to 1. Endosexes were comparable to the male and female genders of typical humanoids. From an evolutionary standpoint, the exosexes were more robust and aggressive than endosexes, and better adapted to handle hunting and gathering while the gentler endosexes stayed in the camp to defend and nurture the young. Exosexes were sallow-skinned and had a variety of eye colors. Endosexes were red-eyed and silver-skinned. (ENT - Rise of the Federation novel: Tower of Babel)
Background
Rise of the Federation: Tower of Babel author Christopher L. Bennett postulates that Jelna have three sex chromosomes X, Y and Z. The four different types of resulting sex are endofemale (X), endomale (XY), exofemale (XZ) and exomale (XYZ), which defined the their prehistoric gender roles: child rearing (endofemale), defending (endomale), gathering (exofemale) and hunting (exomale). Unlike among the four-gendered Andorians and Aenar, only two Jelna contribute genetic material during mating. (Tower of Babel annotations page)
Zami and Kalar
The Zami and their racial sub-group, the Kalar, were a vulcanoid species and as such two-gendered like most baseline humanoids. The Zami sexes were limited to male and female. (ENT - Rise of the Federation novel: Tower of Babel)
Background
The issue of Rigelian sexuality first came up in the ENT episode: "Cogenitor" when Doctor Phlox stated Rigelians had four or five sexes.