Iyaaran

The Iyaarans are a sapient humanoid species from the planet Iyar, whose culture completely lacks concepts such as "pleasure", "antagonism" and "love", which are commonplace to other races. As a result, the Iyaarans find these concepts puzzling and have set up elaborate scenarios to attempt to experience them and comprehend them.

Biology
Members of this species are basically humanoid-looking, with osseous ridges on their foreheads. Unlike most species, they have no cultural concept of "pleasure" (although they're capable of experiencing it) and thus only eat for nourishment, resulting in that their diet consists mostly of bio-enzymatic supplements. They also have no children, as they procreate by what they describe as "post-cellular compounding" and emerge from their natal pods fully-grown.

Iyaaran ambassador Voval once claimed that when a Iyaaran is injured, they enter a state of slowed metabolism to heal themselves; and that this state can easily be mistaken for death by other races. Since this claim turned out to be part of a wider deception, it's not known whether this information is true, although there's nothing to suggest that it isn't.

Culture and society
Their technology includes means to assume an illusory appearance.

Appearances

 * Star Trek: The Next Generation, s07e02, "Liaisons" (1993)