From: Star Trek: The Next Generation
Caption: The Betazoid ambassador Lwaxana Troi
A Federation race basically humanoid except for the solid-colored dark pupils and mental power of telepathy within the race. They also have varying empathic links to other races.
Their empathic/telepathic contact leads to a natural trait of complete honesty, somewhat troubling to outworlders when practiced fully. The telepathy is not inborn but almost always comes on with adolescence. There are also cases of over-empathic abilities, and those who suffer from such extremes must be counseled and trained to avoid insanity, but are almost always affected throughout their life.
Betazoids are actually uncomfortable around those, like the Ferengi and Breen, whose minds they cannot read. Similarly, the minds of animals can be a bit frightening to them, and they tend to prefer smaller animals. Their mind contains the paracortex, their telepathic lobe, which is highly capable of recovery from injury, and includes the "metaconsciousness," or a trauma filter. Psilosynine is the neurotransmitter involved. In addition, their REM sleep frequency is different than for most humanoids.
Betazoids practice an old style of marriage arrangement called genetic bonding, wherein children are promised to each other for marriage later by their parents. On the same note, Betazoids are known for their ability to love more than one person without losing their ability to love their mate, nor are they bound by their marriage customs. Because marriage is a celebration of the act of love to Betazoids, the wedding ceremony itself is traditionally conducted in the nude.
Childbearing is similar to humans, except the normal gestation rate for Betazoid females is ten months rather than nine. Betazoid women are not considered to be "matured" until they at least reach their forties in equivalent human years, which coincides with the timing of the female Betazoid "Phase."